Complex Scenarios with Fig and Vagrant

Many development and test environments consist of more than one service, which sometimes requires a complex configuration or a connection to other services. Although you can easily define images with Dockerfiles, executing them sometimes requires custom scripts and long command lines so that the links between different container volumes work properly.

Luckily, provisioning tools like Fig configure the individual containers with the parameters provided by a configuration file in YAML format [5]. The instances are then provisioned and managed using the fig command-line tool [6]. Listing 8 shows the configuration for the OwnCloud scenario; Listing 9 shows the directory tree of the configuration files – just as a reminder.

Fig is similar to the popular deployment tool Vagrant [7], but it is specifically tailored for Docker. For example, the fig up command would build the images in the mysql and httpd folders on the basis of the given fig.yml file, if they do not already exist, and then start the containers with the defined parameters.

Access should be possible via http://$host-ip/owncloud. Figure 3 shows the OwnCloud setup routine given a correct configuration of the installation. Fig renames the images following a pattern of main_directory_container-name. In this example, the build with fig build would result in two images named owncloud_database and owncloud_httpd.

Figure 3: The OwnCloud setup routine after deployment.

The container itself uses the image name with a serial number as a suffix. If a horizontally scalable application exists in the container, the admin can also use the fig scale command to define how many containers of one type (e.g., httpd) Docker starts. As in docker run -d, fig up -d can start the entire environment in the background. The cleanup command team comprises fig kill and fig rm.

Conclusion

The Docker container system is getting lots of coverage in the press, but if you decide to implement Docker for your own cloud configuration, you'll need more than headlines. In this article, we offered a glimpse at the practical side of deploying Docker in a cloud environment – in this case, the OwnCloud environment. The details for configuring Docker for other clouds are similar. See the article on the CoreOS Linux system, which is designed to support Docker configurations, elsewhere in this issue.