We’ll show you, how to use CentOS crontab. How to automate system tasks on CentOS 7, using Centos crontab. Crontab software utility, is a time-based job scheduler in Unix-like operating systems. Cron is driven by a crontab (cron table) file, a configuration file that specifies shell commands to run periodically on a given schedule. The crontab files are stored where the lists of jobs and other instructions to the cron daemon are kept. Users can have their own individual crontab files and often there is a system-wide crontab file (usually in /etc or a subdirectory of /etc) that only system administrators can edit.
1. Connect via SSH and update the system software
First of all, connect to your Linux VPS via SSH and update all your system software to the latest version available. You can use the following command to do that:
sudo yum update
2. Verify if cronie package is installed
To automate the system tasks, or better known as jobs under Linux, you can use an utility called Cron. Using Cron you can run scripts automatically within a specified period of time, create backup of your databases or other important files, monitor the services running on your server and many other things. To use the Cron utility, you need to install the cronie package on your system. It should be already installed on your server. To confirm, issue the following command:
sudo rpm -q cronie
3. Install cronie package
If it is not installed, you can use yum to install it. Yum is a package manager which you can use to install and manage software on CentOS 7. Run the command below:
sudo yum install cronie
4. Check if crond service is running
The cron jobs are picked by the crond service. To check whether the crond service is running on your CentOS VPS, you can use the following command:
sudo systemctl status crond.service
5. Configure cron jobs
To configure cron jobs you need to modify the /etc/crontab file. Please note that it can only be modified by the root user. To check the current configuration, you can use the following command:
sudo cat /etc/crontab
The output should be similar to the one below:
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# For details see man 4 crontabs
# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * user-name command to be executed
37 * * * * root run-parts /etc/cron.hourly
23 5 * * * root run-parts /etc/cron.daily
19 3 * * 0 root run-parts /etc/cron.weekly
23 0 6 * * root run-parts /etc/cron.monthly
As you can see the crontab file already contain explanation about how to define your own jobs. The syntax is the following:
minute hour day month day_of_week username command
An asterisk (*) in the crontab can be used to specify all valid values, so if you like command to be executed every day at midnight, you can add the following cron job:
Specific users can create cron jobs too. The cron jobs for specific users are located in /var/spool/cron/username. When you create cron jobs for specific users you do not need to specify the username in the cron job. Therefore the syntax will be like the one below:
minute hour day month day_of_week command
6. Restart the crond service
After you make the changes restart the crond service using the command below:
sudo systemctl restart crond.service
For more information you can check the man pages:
man cron
and
man crontab
If it is difficult for you to set up correct cron jobs at the beginning, you can use some cron job calculator to generate the cron job expression. There are several good cron job calculators available on the Internet.
Of course you don’t have to use CentOs crontab, if you use one of our CentOS VPS hosting services, in which case you can simply ask our expert Linux admins to help you with crontab on CentOS to Automate system tasks. They are available 24×7 and will take care of your request immediately.
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Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
Defining a “virtual” constructor.
The new operator considered harmful.
Problem
A framework needs to standardize the architectural model for a range of applications, but allow for individual applications to define their own domain objects and provide for their instantiation.
Discussion
Factory Method is to creating objects as Template Method is to implementing an algorithm. A superclass specifies all standard and generic behavior (using pure virtual “placeholders” for creation steps), and then delegates the creation details to subclasses that are supplied by the client.
Factory Method makes a design more customizable and only a little more complicated. Other design patterns require new classes, whereas Factory Method only requires a new operation.
People often use Factory Method as the standard way to create objects; but it isn’t necessary if: the class that’s instantiated never changes, or instantiation takes place in an operation that subclasses can easily override (such as an initialization operation).
Factory Method is similar to Abstract Factory but without the emphasis on families.
Factory Methods are routinely specified by an architectural framework, and then implemented by the user of the framework.
Structure
The implementation of Factory Method discussed in the Gang of Four (below) largely overlaps with that of Abstract Factory. For that reason, the presentation in this chapter focuses on the approach that has become popular since.
An increasingly popular definition of factory method is: a static method of a class that returns an object of that class’ type. But unlike a constructor, the actual object it returns might be an instance of a subclass. Unlike a constructor, an existing object might be reused, instead of a new object created. Unlike a constructor, factory methods can have different and more descriptive names (e.g. Color.make_RGB_color(float red, float green, float blue) andColor.make_HSB_color(float hue, float saturation, float brightness)
The client is totally decoupled from the implementation details of derived classes. Polymorphic creation is now possible.
Example
The Factory Method defines an interface for creating objects, but lets subclasses decide which classes to instantiate. Injection molding presses demonstrate this pattern. Manufacturers of plastic toys process plastic molding powder, and inject the plastic into molds of the desired shapes. The class of toy (car, action figure, etc.) is determined by the mold.
Check list
If you have an inheritance hierarchy that exercises polymorphism, consider adding a polymorphic creation capability by defining a static factory method in the base class.
Design the arguments to the factory method. What qualities or characteristics are necessary and sufficient to identify the correct derived class to instantiate?
Consider designing an internal “object pool” that will allow objects to be reused instead of created from scratch.
Consider making all constructors private or protected.
Rules of thumb
Abstract Factory classes are often implemented with Factory Methods, but they can be implemented using Prototype.
Factory Methods are usually called within Template Methods.
Factory Method: creation through inheritance. Prototype: creation through delegation.
Often, designs start out using Factory Method (less complicated, more customizable, subclasses proliferate) and evolve toward Abstract Factory, Prototype, or Builder (more flexible, more complex) as the designer discovers where more flexibility is needed.
Prototype doesn’t require subclassing, but it does require an Initialize operation. Factory Method requires subclassing, but doesn’t require Initialize.
The advantage of a Factory Method is that it can return the same instance multiple times, or can return a subclass rather than an object of that exact type.
Some Factory Method advocates recommend that as a matter of language design (or failing that, as a matter of style) absolutely all constructors should be private or protected. It’s no one else’s business whether a class manufactures a new object or recycles an old one.
The new operator considered harmful. There is a difference between requesting an object and creating one. The new operator always creates an object, and fails to encapsulate object creation. A Factory Method enforces that encapsulation, and allows an object to be requested without inextricable coupling to the act of creation.
Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
Wrap a complicated subsystem with a simpler interface.
Problem
A segment of the client community needs a simplified interface to the overall functionality of a complex subsystem.
Discussion
Facade discusses encapsulating a complex subsystem within a single interface object. This reduces the learning curve necessary to successfully leverage the subsystem. It also promotes decoupling the subsystem from its potentially many clients. On the other hand, if the Facade is the only access point for the subsystem, it will limit the features and flexibility that “power users” may need.
The Facade object should be a fairly simple advocate or facilitator. It should not become an all-knowing oracle or “god” object.
Structure
Facade takes a “riddle wrapped in an enigma shrouded in mystery”, and interjects a wrapper that tames the amorphous and inscrutable mass of software.
SubsystemOne and SubsystemThree do not interact with the internal components of SubsystemTwo. They use the SubsystemTwoWrapper “facade” (i.e. the higher level abstraction).
Example
The Facade defines a unified, higher level interface to a subsystem that makes it easier to use. Consumers encounter a Facade when ordering from a catalog. The consumer calls one number and speaks with a customer service representative. The customer service representative acts as a Facade, providing an interface to the order fulfillment department, the billing department, and the shipping department.
Check list
Identify a simpler, unified interface for the subsystem or component.
Design a ‘wrapper’ class that encapsulates the subsystem.
The facade/wrapper captures the complexity and collaborations of the component, and delegates to the appropriate methods.
The client uses (is coupled to) the Facade only.
Consider whether additional Facades would add value.
Rules of thumb
Facade defines a new interface, whereas Adapter uses an old interface. Remember that Adapter makes two existing interfaces work together as opposed to defining an entirely new one.
Whereas Flyweight shows how to make lots of little objects, Facade shows how to make a single object represent an entire subsystem.
Mediator is similar to Facade in that it abstracts functionality of existing classes. Mediator abstracts/centralizes arbitrary communications between colleague objects. It routinely “adds value”, and it is known/referenced by the colleague objects. In contrast, Facade defines a simpler interface to a subsystem, it doesn’t add new functionality, and it is not known by the subsystem classes.
Abstract Factory can be used as an alternative to Facade to hide platform-specific classes.
Facade objects are often Singletons because only one Facade object is required.
Adapter and Facade are both wrappers; but they are different kinds of wrappers. The intent of Facade is to produce a simpler interface, and the intent of Adapter is to design to an existing interface. While Facade routinely wraps multiple objects and Adapter wraps a single object; Facade could front-end a single complex object and Adapter could wrap several legacy objects.
Question: So the way to tell the difference between the Adapter pattern and the Facade pattern is that the Adapter wraps one class and the Facade may represent many classes?
Answer: No! Remember, the Adapter pattern changes the interface of one or more classes into one interface that a client is expecting. While most textbook examples show the adapter adapting one class, you may need to adapt many classes to provide the interface a client is coded to. Likewise, a Facade may provide a simplified interface to a single class with a very complex interface. The difference between the two is not in terms of how many classes they “wrap”, it is in their intent.
There is nothing more excited then try to build your own ecommerce store. Installing OpenCart extensions and themes, modificate them to your need and learn new thing during development. But most OpenCart users know how frustrating it can be get an unexpected error and not be able to find a solution for it.
Most OpenCart issues are solvable. If you got an error, don’t fret because other OpenCart user had the same problem and already gotten it solved. This tutorial collecting most common errors that repeatedly asked by OpenCart users at community forum. Sometime the same error have different error messages, that why we organize the error variant and solution for it.
Before continue, you need to know that an error usually trigger another errors. This is commonly happen because when your code breaks, the rest of code will not work and cause another error. No need to be confuse, the first error is the key. Recognise the error, find issue in your code and try to solve them with solution as suggested on this tutorial.
1. Blank White Pages or 500 Internal Server Error
Blank white pages is a PHP errors that for some reason the error messages isn’t show because your server is not setup to display the errors. While the 500 Internal Server Error means something has gone wrong but the server cannot specifically state what the exact problem is.
The similiarity of both issue is it doesn’t give us a clue what exactly happen, or what files triggering the errors. So, first step before we try to solve the errors is try to show the error messages. Then use the error message as starting point to investigate what is the error cause. Here are a few ways to show the error messages:
Set your “Output Compression Level” to 0 in the System > Settings > Server tab.
Then open php.ini and add code below: 1 2 3 display_errors = 1;error_reporting = E_ALL;log_errors = 1;
If your server not read the php.ini, we will use an alternative method. Open index.php and add code below at the top (line 2): 1 2 3 ini_set('display_errors', 1);ini_set('log_errors', 1);error_reporting(E_ALL);
When you have fixed the problem, remove code line above.
2. Undefined Index / Variable
The error appears when you referencing variable that not been declared. In programming approach set the variable or use isset() to checks if the variable has been set will solve the issue. But for an application to get this issue mean there is a bugs in it, whether it’s OpenCart or extensions files. Or you do some modification on unappropriate way.
Error variant:
PHP Notice: Undefined index: company in /path/public_html/catalog/model/account/customer.php on line 8
PHP Notice: Undefined variable: order_id in /path/public_html/catalog/controller/account/order.php on line 149
PHP Notice: Undefined variable: product in /path/public_html/vqmod/vqcache/vq2-catalog_view_theme_default_template_product_product.tpl on line 272
Solution
If you get this issue on clean OpenCart installation, share the bugs at OpenCart forum. It will help OpenCart developer to develope bugs fix.
When you get this issue after installing an extension, disable the extension then report it to the developer.
If the error refer to file inside the “/vqmod/vqcache” folder, it’s mean the error caused by vQmod file. Disable the vQmod file by rename it to vqmod_file.xml_ and report the bugs to the developer.
3. Undefined Function / Method
If you get “Fatal error: Call to undefined function” or “Fatal error: Call to undefined method” means you try to call the function/ method that doesn’t exist. Commonly happen if files is not uploaded properly or the extensions is not compatible with your OpenCart version; or it’s really doesn’t exist. Here, I will try to classify the problem based on error message.
Error variant:
Related to OpenCart core files
Fatal error: Call to undefined function utf8_strlen() in /path/public_html/system/helper/utf8.php on line 39
Fatal error: Call to undefined method Customer::isLogged() in /path/public_html/catalog/model/catalog/product.php on line 8
Warning: require_once(/path/public_html/system/library/customer.php) [function.require-once]: failed to open stream: No such file or directory in /path/public_html/index.php on line 22
Fatal error: require_once() [function.require]: Failed opening required‘/path/public_html/system/library/customer.php’ (include_path=’.:/usr/lib/php’) in /path/public_html/index.php on line 22
Related to vQmod files
Fatal error: Call to undefined method ModelAccountCustomer::getPaymentAddress() in /path/public_html/vqmod/vqcache/vq2-catalog_controller_checkout_confirm.php on line 38
Related to PHP built-in functions
Fatal error: Call to undefined function imagecreatefromjpeg() in /path/public_html/system/library/image.php on line 34
Fatal error: Call to undefined function mysql_connect() in /path/public_html/system/database/mysql.php on line 6
Solution
Related to OpenCart core files
Some file is not uploaded or it’s corrupted during upload process. Reupload the files to your server with ASCII mode, not binary.
In some case, this issue appear because server path is not configured properly at config.php. So recheck your server path in config.php and admin/cofig.php
“Warning/ Fatal error: require_once” mean the file is not available. You need to reupload the file mentioned on the error message or fix the server path at config.php as mentioned above.
Related to vQmod files
vQmod fails to generate new cache from the extensions vQmod files. Check vqmod/cachefolder permission, make sure it’s writable and clear all cache files.
Enabled / disabled one by one vQmod files you have. Once you get the cause, contact the developer.
The extensions is not compatible with your OpenCart version or it have a bug. Contact the developer.
Related to PHP built-in functions
PHP have lot of built-in functions, you can check it here. Errors related to PHP built-in function is server issues. Contact your host to solve this.
4. Headers Already Sent
You get an error message “headers already sent” right after installing, modificating, updating OpenCart or vQmod files. There is a good refference explaining the issue.
Error variant:
Warning: Cannot modify header information – headers already sent by (output started at /path/public_html/config.php:31) in /path/public_html/index.php on line 175.
Warning: session_start() [function.session-start]: Cannot send session cookie – headers already sent by (output started at /path/public_html/config.php:31) in /path/public_html/system/library/session.php on line 11.
Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /path/public_html/config.php:31) in /path/public_html/system/library/session.php on line 11.
Solution:
Download the file stated at the error message then apply solution bellow:
Remove spaces at begining and end of file. 1 2 3 <?php //contain spaceecho"remove all space or line-break before <?php and after ?>";?>
Resave the file with Notepad++ or other editor (encode file as ANSI or UTF-8 without BOM).
Reupload to server through FTP in ASCII mode, not binary.
5. Session Issue
PHP session store user information on the server for later use (i.e. login status, shopping items, etc) across the page requests. Session is temporary information and will be deleted after the user left the website. OpenCart use session on lot of aspect like login status, product cart, compare etc. In most case, session issue will throw error messages. But there is time when it’s not show any error message; to recognise it, here is some indication of session issue:
Product on the cart is self-cleared.
Product on the cart is cleared after user logged in.
No items stored at product compares.
OpenCart admin always asking to login and get message “Invalid token session. Please login again”.
Error variant:
Warning: session_start () [function.session-start]: open (/tmp/sess_41abirkdiesf9efwej46wtib2, O_RDWR) failed: No such file or directory (2) in /path/public_html/system /library /session.php on line 11
Warning: session_start () [function.session-start]: open (/tmp/sess_41abirkdiesf9efwej46wtib2, O_RDWR) failed: Permission denied (13) in /path/public_html/system /library /session.php on line 11
Warning: session_start() [function.session-start]: open(/tmp/sess_41abirkdiesf9efwej46wtib2, O_RDWR) failed: No space left on device (28) in /path/public_html/upload/system/library/session.php on line 11
Solution:
No such file or directory issue
Open php.ini and add code below: 1 session.save_path = /tmp;
If solution above not work, contact your host and ask them how to set session.save_path.
Other errors
“Permission denied”, ask your hosting to check the session directory permission.
“No space left on device”, ask your hosting is it server issue or you need to upgrade to larger hosting space.
6. Allowed Memory Size Exhausted
This error happen because your memory is not enough to execute the php code (uploading large image, delete lot of products, send mass mails etc). Increasing the memory allocated for PHP will solve the issue.
Error variant:
Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 47200 bytes) in /path/public_html/system/library/image.php on line 34
Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 13069817 bytes) in /path/public_html/system/library/mail.php on line 144
Fatal error: Out of memory (allocated 33554432) (tried to allocate 14024 bytes) in /path/public_html/library/image.php on line 34
Solution:
Apply one of solutions bellow to increasing the limit to 64MB, 128MB, 256MB or 512MB -depends on your host.
Edit php.ini 1 memory_limit = 128M;
Or put code below to .htaccess 1 php_value memory_limit 128M
If you oftenly get this error and solution above isn’t work, contact your host. In most shared hosting, there is maximum memory_limit. You can’t set memory-limit to 64Mb if you get max 32Mb.
7. Restriction in effect
You get an error message “SAFE MODE Restriction in effect”. This is a PHP restriction issue, and your server account is trying to run a -builtin PHP- functions but doesn’t have access to run it. This issue is nothing to do with OpenCart, but related to your server configuration.
Error variant:
Warning: session_start() [function.session-start]: SAFE MODE Restriction in effect. The script whose uid is 10025 is not allowed to access /path/public_html/system/library/session.php on line 11
Warning: imagejpeg() [function.imagejpeg]: SAFE MODE Restriction in effect. The script whose uid is 10305 is not allowed to access /path/public_html/image/cache/data owned by uid 48 in /path/public_html/system/library/image.php on line 44
Warning: is_dir(): open_basedir restriction in effect. File(/path/public_html/image/87cngmlc22pe96fof5fhmq9c290phri7) is not within the allowed path(s): (/path/server/) in /path/public_html/catalog/controller/checkout/confirm.php on line 248
Solution
Safe Mode and open_basedir restriction is a server issue, ask your host to turn off the restriction is the best way to fix the issue.
But in case you wanna try to resolve it, try this solution: 1 2 3 4 5 6 7 // Put code bellow at php.inisafe_mode = Off;--- or---// Put code bellow at .htaccessphp_value safe_mode off
Usefull Tools
System Information
System Information provide server information, PHP built-in functions and file/ folder permission that required or recomended by OpenCart. This extension will help you to monitor that your site / server meet OpenCart requirements to work well. You can download it at OpenCart Marketplace.
vQmod Manager
vQmod Manager allows users to managing vQmod files. This extension display vQmod file information and help you to manage (Upload, delete, install, uninstall and backup) and monitor the vQmod files through the admin panel. You can download it at OpenCart Marketplace.
Do you experience application hang problems? If so, read this article to discover the top 3 reasons applications hang and cause slow performance.
If you have been in the IT industry long enough, you probably know this story well. The application works fine, then, suddenly, the application hangs with no apparent reason. You restart the application and it all goes away.A week passes, maybe two, and then the application hangs again. Another restart and you’re back. It doesn’t crash or fail (no crash dump or thread dump)—it just sits there and hangs. No users are being served.
Eventually you decide to just restart every night hoping it will not hang again. It doesn’t matter if you’re using a Tomcat application server, WebSphere, WebLogic, JBoss or whatever — if you have been in the software development business long enough, you must have experienced this problem. This is where application monitoring can help.
Below are the top 3 reasons why an application server hangs:
Reason #1: it’s a database problem.
This may sound strange, but the main reason an application server hangs is not directly related to the application server itself. The location of the symptom is rarely the location of the root cause. The following scenario is quite common:
The database is bottlenecked, causing queries to run slower than usual.
Requests that used to take 1 second, now take 5 seconds to complete.
The average number of concurrent requests slowly increases (due to backlog).
The server runs out of threads and the application server hangs.
If you manage to get a thread dump, you’ll just see a bunch of threads waiting and another group that’s actually running. Another possibility is that the number of waiting threads (or queued threads) will gobble up all available memory and, eventually, lead to an OutOfMemory error.
Reason #2: deadlocks.
If it seems that the application server is doing nothing, look for deadlocks. These can be database deadlocks that cause your SQL queries to hang, or seek the update statements. For example, a transaction log that is written to the database for each request may easily hang the entire application if the log table is locked. It can also be a deadlock of the application re-accessing itself. Do you have any HTTP SOAP calls from one application server to another? Also check for shared objects—an operating system file that is written to from multiple threads at once.
Reason #3: run-away thread.
In cases where the application server is indeed to blame, you should look for a run-away thread. These are hard to detect because they hardly show up on logs since they are usually only written when the request has completed. A run-away thread will probably not return until it has already affected the entire application. Therefore, the hanging request will not be written to the log. These ‘runaway’ threads typically include infinite loops in code. For example, a query that should show results that does not include the option of paging between result pages suddenly needs to display a large number of results. The page takes forever to render and clobbers the application server, eventually causing it to hang.
These types of application hangs are extremely difficult to diagnose and detect. The hardest part is isolating the root cause of the problem. If the application server hangs, it doesn’t necessarily mean that the problem resides there. It usually doesn’t. End-to-end transaction management tools, such as SharePath by Correlsense, helps to pinpoint the reasons for an application hang by providing a real-time view into the entire application behavior.
Laravel utilizes Composer to manage its dependencies. First, download a copy of the composer.phar. Once you have the PHAR archive, you can either keep it in your local project directory or move to usr/local/bin to use it globally on your system. On Windows, you can use the Composer Windows installer.
First, download the Laravel installer using Composer.
composer global require "laravel/installer=~1.1"
Make sure to place the ~/.composer/vendor/bin directory in your PATH so the laravelexecutable is found when you run the laravel command in your terminal.
Once installed, the simple laravel new command will create a fresh Laravel installation in the directory you specify. For instance, laravel new blog would create a directory named blog containing a fresh Laravel installation with all dependencies installed. This method of installation is much faster than installing via Composer.
Via Composer Create-Project
You may also install Laravel by issuing the Composer create-project command in your terminal:
Once Composer is installed, download the 4.2 version of the Laravel framework and extract its contents into a directory on your server. Next, in the root of your Laravel application, run the php composer.phar install (or composer install) command to install all of the framework’s dependencies. This process requires Git to be installed on the server to successfully complete the installation.
If you want to update the Laravel framework, you may issue the php composer.phar updatecommand.
The Laravel framework has a few system requirements:
PHP >= 5.4
MCrypt PHP Extension
As of PHP 5.5, some OS distributions may require you to manually install the PHP JSON extension. When using Ubuntu, this can be done via apt-get install php5-json.
The first thing you should do after installing Laravel is set your application key to a random string. If you installed Laravel via Composer, this key has probably already been set for you by the key:generate command. Typically, this string should be 32 characters long. The key can be set in the app.php configuration file. If the application key is not set, your user sessions and other encrypted data will not be secure.
Laravel needs almost no other configuration out of the box. You are free to get started developing! However, you may wish to review the app/config/app.php file and its documentation. It contains several options such as timezone and locale that you may wish to change according to your application.
Once Laravel is installed, you should also configure your local environment. This will allow you to receive detailed error messages when developing on your local machine. By default, detailed error reporting is disabled in your production configuration file.
Note: You should never have app.debug set to true for a production application. Never, ever do it.
Permissions
Laravel may require one set of permissions to be configured: folders within app/storagerequire write access by the web server.
Paths
Several of the framework directory paths are configurable. To change the location of these directories, check out the bootstrap/paths.php file.
The framework ships with a public/.htaccess file that is used to allow URLs without index.php. If you use Apache to serve your Laravel application, be sure to enable the mod_rewrite module.
If the .htaccess file that ships with Laravel does not work with your Apache installation, try this one:
6 Essential Tips on How to Become a Full Stack Developer
How to become a full stack developer? As one of the hottest topics for developers, the discussions have never stopped. On LinkedIn and Facebook, lots of people put their job title as a full stack developer. Besides, it seems that the “Full Stack” topic has already become a new job trend. An article on Medium has discussed the full stack designer getting both praise and blame. Some people think that the full stack is just a title, what he/she should focus on is the real personal ability and technology.
Essentially, I think the discussion about the full stack is also a kind of argument relating to the all-rounder and expert in the IT industry, and debate on the depth and breadth of development skills.
You can’t have your cake and eat it too. While the full stack developers and full stack designers seem like they are challenging this possibility. Because their horizontal skills tree gives them the ability to both have and eat the cake. There is another saying is that jack of all trades, but master of none. So it’s necessary to think about how to become a real full stack developer but not an empty title.
1. What is a full stack developer?
Simply put, full stack developer is a kind of people who master a variety of skills and use these skills to complete a product independently. A top voted answer on Quora explained that what is a full stack developer:
A full stack developer is an engineer who can handle all the work of databases, servers, systems engineering, and clients. Depending on the project, what customers need may be a mobile stack, a Web stack, or a native application stack.
In fact, “full stack” refers to the collection of a series of technologies needed to complete a project. “Stack” refers to a collection of sub-modules. These software sub-modules or components combined together to achieve the established function while without the need for other modules.
2. Why has the full stack developer been controversially discussed?
As it mentioned above, the discussion about full stack developer is actually the debate on the depth and breadth of skills. Especially at the OSCON conference, a Facebook engineer said they only hired a “full stack developer.” This topic came as a result of a heated discussion about the strengths and weaknesses of being a full stack developer.
Advantages: The full stack developers involved in a horizontal technical requirement, so that he/she can make a prototype design for a product very rapidly with his wide range of techniques. With the full stackability, they have a broader angle of views and a more active mindset. Moreover, they will be more sensitive to techniques and products. So, this kind of people can always have his/her opinions towards the product or design.
From another aspect, he/she can provide help to everyone in the team and greatly reduce the time and technical costs of team communication, technology docking. So many of them become entrepreneurs or as technical partners in start-up companies.
Disadvantages: It is precisely because of the horizontal technology development, some the full stack developers cannot be expert in one skill. Most of them who claim to be “full stacks developer” are only know a little about the multiple skills. As for how to make the architecture more suitable for the modular development, that’s a question.
3. Even so, there are still people asking, how to become a full stack developer?
A qualified full stack developer should have functional knowledge and capabilities for all aspects involved in building the application.
1) Programming languages
You need to be proficient in multiple programming languages, such as JAVA, PHP, C #, Python, Ruby, Perl, etc. As most of your core business processes need to be written in these languages.Maybe not all need. But you also have to master the language grammar, and to be very familiar with how to structure, design, implementation, and testing of the project based on one language or more languages. For example, if you choose JAVA, then you need to master the object-oriented design and development, design patterns, J2EE-based components of the development and so on.
Where to learn: Git/GitHub — You have to know how to use Git to manage and share your code.
2) Use development frameworks and third-party libraries
The popular development languages are generally accompanied by a good development framework, such as JAVA Spring, MyBatis, Hibernate, Python Django, PHP thinkphp, yin, nodeJs express and so on.
Front-end technologies are becoming more and more important in today’s project and product development. In addition to product features, the user experience is also one of the criteria to test the success of a product. All that depends on the implementation of the front-end technology, soyou need to master some basic front-end technologies such as HTML5, CSS3, JavaScript, and further study the front-end frameworks or third-party libraries such as JQuery, LESS, SASS, AngularJS, or REACT.
Any product or project needs a database to store data. As a full stack developer, you also need to have at least one or two databases and know how to interact with the database. Currently, the popular database is MySQL, MongoDB, Redis, Oracle, SQLServer and so on. As a document-type database, MongoDB, is being used more widely in Internet products. As for larger projects, Ialso recommend using MySQL or commercial Oracle as the back-end database. While memory databases, such as Redis, can be used for caching to improve system performance.
Most of the articles or discussions about the full stack developer are rarely related to the design requirements. But I think the design skill is very important, the principle and skill of basic prototype design, UI design, UX design are also needed to understand.
6) Self-requirements are also an essential factor to become a full stack developer:
Global thinking
Good communication skills
Creativity
Curiosity
Time management skills
Wrap Up
According to Gladwell’s 10,000 hours of law, it will spend 10 years to master the front-end, back-end, client-oriented knowledge content to be a full stack developer. Therefore, the full stack developer is by no means to accomplished overnight. What you need to do is laying the technical foundation, strengthen the core skills, and keep learning for more challenges.
What does the term “full-stack programmer” mean? What are the defining traits of a full-stack programmer?
A full stack developer is capable of performing tasks at any level of the technical stack in which they reside. It means:
Working with systems infrastructure (knowing what hardware to ask for , what OS to install, how to prepare the system and dependencies for all software)
Understanding, creating, manipulating, and querying databases
API / back-end code in one or more languages, e.g. Ruby, Java, Python, etc.
Front-end code in one or more languages, e.g. HTML, JavaScript, Java, etc.
Project management / client work, e.g. gathering requirements, creating technical specifications and architecture documents, creating good documentation, managing a project timeline (e.g., someone who knows Agile/SCRUM/Kanban)
In general a full-stack developer has knowledge that is a mile wide, but not necessarily very deep, and has core competencies in the pieces of the stack in which they work most. In my work I have core competencies in Linux (Debian, CentOS, Amazon Linux), Database design, manipulation, and query (PSQL and MySQL), back-end technologies (Java, Ruby, and Python), and some front-end design (HTML, vanilla JavaScript, and jQuery), as well as act as SCRUM-master and lead Agile development for my team, interfacing with clients both internal and external to the business to gather requirements, execute tasks, and document all efforts.
Typically these skills are developed over many years in the contexts of different jobs, so as Ian mentioned being a full-stack developer means being pushed outside of your comfort zone to constantly learn new skills.
The easiest way to generate random rows in MySQL is to use the ORDER BY RAND() clause.
SELECT col1 FROM tbl ORDER BY RAND() LIMIT 10;
This can work fine for small tables. However, for big table, it will have a serious performance problem as in order to generate the list of random rows, MySQL need to assign random number to each row and then sort them. Even if you want only 10 random rows from a set of 100k rows, MySQL need to sort all the 100k rows and then, extract only 10 of them.
My solution for this problem, is to use RAND in the WHERE clause and not in the ORDER BY clause. First, you need to calculate the fragment of your desired result set rows number from the total rows in your table. Second, use this fragment in the WHERE clause and ask only for RAND numbers that smallest (or equal) from this fragment.
For example, suppose you have a table with 200K rows and you need only 100 random rows from the table. The fragment of the result set from the total rows is: 100 / 200k = 0.0005. The query will look like:
SELECT col1 FROM tbl WHERE RAND()<=0.0005;
In order to get exactly 100 row in the result set, we can increase the fragment number a bit and limit the query: For example:
SELECT col1 FROM tbl WHERE RAND()<=0.0006 limit 100;
