DEV Community: Akshay

Rearranging application instances in Passenger.

Akshay — Sat, 04 Sep 2021 10:12:47 +0000

Problem: We had three internal rails applications running in one physical serve. During some of the deployments, one of the applications was not booting up. Though occurrence of such an event was very low I looked into the issue as it stimulated me.

We had a master passenger.conf and each application had their own application.conf, which looked something like this:

Master

PassengerRoot /usr/local/rvm/gems/ruby-2.6.0/gems/passenger-6.0.2
PassengerDefaultRuby /usr/local/rvm/gems/ruby-2.6.0/wrappers/ruby
PassengerMaxPoolSize 18
PassengerPoolIdleTime 300

Application specific configs

PassengerAppEnv qa
PassengerRuby /usr/local/rvm/gems/gemset/wrappers/ruby
PassengerMinInstances 9
PassengerPreStart http://localhost:81/

If we carefully look at the PassengerMaxPoolSize and PassengerMinInstances for three applications, they didn't add up. Forget request load balancing, passenger didn't even have space for booting the application because Max was set to 18 and each application's min was 9. This meant, at any given time there could be only two applications running.

Fortunately, that wasn't the case. The deployment sequence decided the number of instances of each application that will occupy the 18 available slots. If all the three were deployed simultaneously then each occupied x,y,z number of instances based on the application's booting time.

Some of the examples of numbers were:

x	y	z
6	9	3
9	5	4
9	9	0

Solution: We had to change PassengerMinInstances to a number that was suitable for the application. It was also made sure that passenger get a couple of free instances for Request load balancing.

Multiple Jenkins files in a single git repository

Akshay — Sat, 04 Sep 2021 10:08:51 +0000

We have a single git repository under which 2 applications run. To build a separate pipeline for both the projects using Jenkinsfile, under the application folders I created a Jenkinsfile and did the following in the UI

Job configuration -> Build Configuration -> Script -> {ApplicationName}/Jenkinsfiles

Installing MariaDB inside a container

Akshay — Sat, 04 Sep 2021 10:07:46 +0000

We had a requirement of installing MariaDB to an existing docker image because the test cases had to run within the same image and the rails framework needs a test database to run the tests.

After installing the MariaDB using yum, we tried to start the sql server within the container, it threw

ERROR 2002 (HY000): Cant connect to local MySQL server through socket /var/lib/mysql/mysql.sock

Excerpts of step from the article:

start the service manually and
ensure that you have started it such that it will stay in the foreground (because a Docker container exits when the foreground process exits or puts itself into the background).
Inside a docker container, nothing will run by default. The following code when executed within the container will start the server.

/usr/libexec/mariadb-prepare-db-dir mariadb.service 

/usr/bin/mysqld_safe --basedir=/usr &

We added these lines to our Dockerfile and every time sql-server was started during the boot up.