Subordinate Services

[Benjamin Saller]

One of the highly requested features for Juju has landed along side
the 12.04 release of Ubuntu, subordinate services.
Complete documentation is available at::

    https://juju.ubuntu.com/docs/subordinate-services.html

This feature is designed to allow a new class of services that run in
the same deployment as other service.  Subordinate
services allow for units of different services to be deployed into the
same container as a traditional service and for them
to have knowledge of each other. Charms deployed inside the container
of another service are called subordinates and the
services containing a subordinate is a principal.

Good use cases or this feature might include things like log
aggregation, monitoring support or making customizations
to the container of another service. This feature isn't about
achieving high machine utilization but rather allows for services
that need access to the filesystem of another service.

When trying to understand how to take advantage of this feature it is
important to understand (in addition to previous knowledge
about authoring charms), implicit interfaces and in turn container
relations (described in the previous link).

    https://juju.ubuntu.com/docs/implicit-relations.html

Implicit relations will allow charm authors to establish relations
with principal services that have no special knowledge about
subordinates deployed with them. This is done by forming a container
relationship with a relation provided by all charms.

We look forward to new charms using this feature, as always help is
available on this mailing list and on IRC at FreeNode/#juju.

Enjoy,
-bcsaller