Configuring Capistrano to run migrations on multiple servers

 

A few months ago I found myself in a situation where I had to run the migrations on a second server. After some research, I learned that Capistrano only runs migrations on the first server in the :db group, so other servers with :db will be ignored.

I was very surprised!!!

I kept looking into this and finally found the option I was looking for:

This is an example of the config/deploy/production.rb

 server 'sample-web-server1', user: 'deploy', roles: %w{app web db}
 server 'sample-web-server2', user: 'deploy', roles: %w{app web}
 server 'sample-web-server3', user: 'deploy', roles: %w{app web db}

Now in your config/deploy.rb file add this option:

 set :migration_servers, -> { release_roles(fetch(:migration_role)) }

Now, you just have to deploy.

As a side note:

According to the capistrano changelogs, this option was introduced from version 1.1.7, so if you have capistrano 1.1.7 onwards, you can safely use it. 

You can also check the capistrano documentation here

Useful Mysql Queries

 

There are some situations where your application could crash and sometimes the problem is not really in the source code, but in the database. e.g: you are using wrong collation for a specific table or column or maybe you are using wrong data type etc.

These Mysql statements can help you debug or better understand your current database structure.

Let's begin:

1.  Show all columns for a specific table:

 SHOW COLUMNS FROM users;

output:

and also you can filter by field or type etc.

 SHOW COLUMNS FROM users WHERE field = 'email';

2. Show table details:

 SHOW TABLE STATUS;

output:

and of course you can filter by table name:

 SHOW TABLE STATUS where name = 'users';

Output:

3. Show Mysql variables:

 SHOW variables;

output:

and also you filter by variable name:

 SHOW variables WHERE Variable_name =  'max_allowed_packet';

4. Show Table size:

 SELECT TABLE_NAME AS `users`, ROUND((DATA_LENGTH + INDEX_LENGTH) / 1024 / 1024) AS `Size (MB)` FROM information_schema.TABLES WHERE TABLE_NAME = "users" AND TABLE_SCHEMA = 'my_blog'

Output:

More are coming soon..

Ubuntu: How to install an old Firefox version

If you want to install an old version of Firefox, you just have to follow these steps:

In this case, I had Firefox 4.5.0 and now I want to install Firefox 47.0.1


First, open your terminal

1. Download firefox 47.0.1
   
   wget https://ftp.mozilla.org/pub/firefox/releases/47.0.1/linux-x86_64/en-US/firefox-47.0.1.tar.bz2
2. Unzip Firefox
   
   tar -xjvf firefox-47.0.1.tar.bz2
3. We remove the old version
   
   sudo rm -rf /opt/firefox*
4. we move the unzip firefox 47.0.1 to the firefox folder
   
   sudo mv firefox /opt/firefox
5. create symbolic link
   
   sudo ln -sf /opt/firefox/firefox /usr/bin/firefox

How to edit a commit message

what you need to do is go to your repository  and type this in your command line:



  git commit --amend



Then in your text editor you can put the new commit message.

Good Luck And Happy Hacking!!!

Git push force

Sometimes, it is  necessary to performed a push force in our repositories, but you need to be really careful because this action will overwrite all, so you need to know what you are doing.

This is the code:

git push -f <remote> <branch>

e.g
git push -f origin my_new_feature

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Jquery DatePicker - How to Reset Date

Sometimes,  when you are working with jquery hiding elements or showing some elements, you might need to reset Datepicker to avoid sending a wrong date.

This code will allow you to reset the date by setting a null value in the date selector

var my_date = $('#my_birthday').datepicker();
$('#btn-clear-date').on('click', function () { my_date.datepicker('setDate', null);
});