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Mark Shuttleworth
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Best we think carefully about how we've created the mess in the Middle East, before we go thugging our way in there again.

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Planning to publish Docker images of your app? Here's how to turn that into a completely reusable part on any cloud, with automated integration defined in a Juju charm.

Ben describes a solution to the very common problem of ordering in orchestration - Docker gives you a neat way to encapsulate the bits, Juju provides the means to integrate them automatically into the overall project. You get all the benefits of Docker and Juju, and a little bit extra from Ben :)
Docker orchestration with Juju

As we scale-out Docker containers its important to make sure that each new container is started with the proper connections and credential information for communicating with its dependencies. In Juju we call the modelling of this flow of information 'Relations'. These are 1st class citizens in our model and can automatically ensure the right information is passed to the proper services, even in the case of horizontal scaling.

Here we've created a pattern that we use a number of places in Juju which encapsulates service restarts to happen only once all of their dependencies have provided all the data they depend on. For example only once your web-app container has been passed the DB connection will the container be started and passed through the firewall. Adding new front-end app containers will likewise obtain their information from the same relationship.

Following our previous experiments with Docker orchestration we've updated the RethinkDB charm to use our services framework. This means that for the most part a single data driven method drives all the Docker orchestration.  If you are unfamiliar with Juju charms you can start by looking at https://github.com/bcsaller/juju-docker/blob/master/hooks/common.py#L39 (the manage method). This single method is called by all the normal Juju lifecycle events and just 'does the right thing'. If others adopt this pattern, some of the helper code here would be moved out of this hook file and directly into charm-helpers (a Python library to help author charms). This would further simplify the orchestration code.

This work expands on what was previously mentioned in
https://plus.google.com/117270619435440230164/posts/XEcbYX5tHBM and includes a number of lessons learned.

We're always interested in feedback (and pull requests!), if you have questionsfeel free to join the juju mailing list or find us on freenodes #juju .

ML: https://lists.ubuntu.com/mailman/listinfo/juju
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