Runninng Docker containers as systemd services

Starting and stopping Docker containers is easy with the docker run and docker {stop|kill} commands. By default, when the Docker daemon is restarted, running containers are also restarted. This is a great feature but sometimes you need more control over the container’s lifecycle.

Imagine having a container which is linked to another one. Docker does not provide any way of specifying which container should be started when or what to do if a container dies.

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Customizing the configuration of the WildFly Docker image

Default configuration is a great place to start with a project. We at JBoss try to make our projects (and products too!) usable out-of-box for as many use cases as we can, but there is no way that one configuration could satisfy everyone’s needs. For example, we ship 4 flavors of the standalone.xml configuration file with WildFly since there are so many different deployment scenarios. But this is still not enough. We need to be able to tweak it at any point. The jboss/wildfly image is not an exception here.

Following the Docker recreate — do not modify principle we do change the configuration by creating a new image (in most cases). This allows us to reuse the images (consider the jboss/wildfly image itself).

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Logging with the WildFly Docker image

There are various ways to set up logging for Docker containers. Docker itself has a built-in logs command, you can mount a volume from the host and save the logs there, you can create a different container that would be only responsible for log handling, or set up a logging daemon. Every method has some pros and cons and it is up to you to choose the one that fits best.

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Creating a minimal WildFly Docker image

The default way of creating an image with Docker is to extend an image by using the FROM call in the Dockerfile. But this is not the only way to do this. You can easily create a base image by using only the yum command.

WildFly 8.0.0.Final was recently released and is now available in Fedora 20 updates-testing repository. Let’s create an image that could be used to test this release but make it as minimal as it could be. The application server does have a lot of dependencies, so do not expect a 100 MB image. It’ll be closer to 1 GB.

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WildFly cluster using Docker on Fedora

In my previous blog post I introduced Docker and its Fedora integration. Now it's time to do some serious (read: useful) stuff.

A few years ago I started a project called CirrAS. It's dead now, but the main idea behind it was to form a cluster of JBoss AS servers in the cloud, without any unnecessary steps. You just launched the instances, they found and connected to each other and the result was a working cluster. Additionally every cluster node registered itself in a front-end instance which worked as a load balancer and monitoring/management (we used RHQ) node.

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