Docker MySQL can't connect to socket - mysql

Question

I'm learning Docker and I've a problem trying to connect a Rails app on the passenger-full container and a mysql container. Both are linked in a compose file
app:
build: ./rails
ports:
- "80:80"
links:
- database
volumes:
- ./rails:/home/app/webapp
database:
image: mysql
environment:
- MYSQL_DATABASE="dockertest"
- MYSQL_USER="dockertest"
- MYSQL_PASSWORD="dockertest"
- MYSQL_ROOT_PASSWORD="root"
So I added the apt-get install at the top of my Dockerfile like this
FROM phusion/passenger-full
RUN apt-get update && apt-get install libmysqlclient-dev mysql-client -y
# Set correct environment variables.
ENV HOME /root
# Use baseimage-docker's init process.
CMD ["/sbin/my_init"]
RUN rm -f /etc/service/nginx/down
RUN rm /etc/nginx/sites-enabled/default
ADD webapp.conf /etc/nginx/sites-enabled/webapp.conf
RUN mkdir /home/app/webapp
WORKDIR /home/app/webapp
ADD . /home/app/webapp
RUN cd /home/app/webapp && bundle install
RUN touch /home/app/webapp/tmp/restart.txt
# Clean up APT when done.
RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
Also this is my database.yml in the Rails app.
default: &default
adapter: mysql2
database: dockertest
host: <%= ENV['MYSQL_PORT_3306_TCP_ADDR'] %>
port: <%= ENV['MYSQL_PORT_3306_TCP_PORT'] %>
username: dockertest
password: dockertest
development:
<<: *default
production:
<<: *default
The problem is that I cant stop receiving the error
Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)
The webconf file is
# /etc/nginx/sites-enabled/webapp.conf:
server {
listen 80;
server_name localhost;
root /home/app/webapp/public;
passenger_enabled on;
passenger_user app;
passenger_ruby /usr/bin/ruby2.2;
}
Is that the right way to do this? As you can see I'm pretty new to docker.

Answer 1

The problem here is with the links directive in your docker-compose.yml file. You have:
links:
- database
That's basically saying that the link name:alias is database:database, according to the docker-compose.yml reference.
Also, if you read the linking container docs you can see that the environments exported to the source container are of the format ALIAS_XXX for example ALIAS_PORT_3306_TCP_PORT. So in essence in your database.yml what you want to do is something like this:
default: &default
adapter: mysql2
database: dockertest
host: <%= ENV['DATABASE_PORT_3306_TCP_ADDR'] %>
port: <%= ENV['DATABASE_PORT_3306_TCP_PORT'] %>
username: dockertest
password: dockertest
development:
<<: *default
production:
<<: *default
If you want to use the MYSQL alias your links would have to look something like this in your docker-compose.yml file.
links:
- database:mysql
The error:
Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)
is basically coming from your Rails app not being to see what's in your database.yml and defaulting to a local /var/run/mysqld/mysqld.sock connection.
Hope it helps.