List of useful Docker commands

In the last few weeks I’ve been doing several experiments with Docker, just trying to grasp the main idea and maybe even come up with something useful.

As often happens with tools these days, there’s an entire world of command line tools that you should learn.

OR you can just be lazy as me and keep a list of the most common ones ๐Ÿ™‚

I’ll be updating this list from time to time, just to keep track of what I’ve used so far and be a quick reference for my sloppy memory.

docker login [HOST] # in case you need auth to pull or push images
docker build -t [TAG]
docker images # shows a list of the local images along with the size
docker push [TAG]
docker system prune -a # this will remove ALL your images and containers. Very useful when you run low on space, but be careful!

The next command will display the Docker daemon logs, extremely useful when you don’t know what happened (basically me most of the time) and you’re looking for an answer, even if obscure.

It depends on the OS you’re running on:

  • Ubuntu (old using upstart ) – /var/log/upstart/docker.log
  • Ubuntu (new using systemd ) – sudo journalctl -fu docker.service
  • Boot2Docker – /var/log/docker.log
  • Debian GNU/Linux – /var/log/daemon.log
  • CentOS – /var/log/daemon.log | grep docker
  • CoreOS – journalctl -u docker.service
  • Fedora – journalctl -u docker.service
  • Red Hat Enterprise Linux Server – /var/log/messages | grep docker
  • OpenSuSE – journalctl -u docker.service
  • OSX – ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/log/dโ€Œโ€‹ocker.log
  • Windows – Get-EventLog -LogName Application -Source Docker -After (Get-Date).AddMinutes(-5) | Sort-Object Time, as mentioned here.

(thanks, Scott)

How to create a docker container for a WordPress website

This is my first post on Docker so please be gentle. I am going to start with something easy: how to create a Docker container to host a WordPress website.

One word before we start: don’t do this on a production server! There are more rules and checks you have to do, this is just an introduction, good for a dev/demo environment.

So, I assume you already have docker and docker-compose installed on your system, but in case you don’t, there’s an excellent documentation on the Docker’s website.

The first step is to fire up the terminal, create a folder and save the contents of this gist to a file named docker-compose.yml .

Next step is to fire up the containers with this command:

docker-compose up -d

the -d is the “detached mode”, allows you to run the containers in background and keep using the terminal.

Now, if you take a look at our Compose configuration, on line 22 we have specified an host address for the mysql instance. It might be already correct, but better check. 
From the command line, first run

docker ps

to get the list of running containers. You should see something like this:

using docker ps to get the list of containers

using docker ps to get the list of containers

Grab the name of the db container and run

docker inspect wptestfull_mysql_1

You will get a big JSON object exposing the status and all the available properties of the container. At the end you should get this:

using docker inspect to get the container ip address

using docker inspect to get the container ip address

there you go, our IPAddress. Copy it into the docker-compose file and run again docker-compose up -d .

Now we need to create a db user. Open your browser and go to http://localhost:8181/ , you will see the phpMyAdmin interface. Create the user, the db and set the allowed hosts to % . This way we will allow connections from every address. Again: don’t do this on production!

Now all you have to do is to load http://localhost:8080/ and setup your WordPress instance ๐Ÿ™‚

Next time: what if we want more than one website?

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