Heterogenous Docker Swarms Teaser

Note: This is all very experimental; Docker does not support any architecture other than X86_64.

The last few evenings I’ve been working on Mulitifarious, a means of creating heterogenous Docker Swarms. I’d previously found that I can create a swarm with heterogenous members — a swarm which has, say, X86_64 and Raspberry Pi members. The problem arose, of course, once I attempted to run containers in the swarm. Containers are architecture specific.

Enter Multifarious. And no, multifarious isn’t nefarious, even if the words sound similar. Rather it means “many varied parts or aspects” (Google)

Multifarious uses dependency injection to tell Docker the name of a container suited to an Architecture.

In the preliminary version, ClusterHQ’s powerstrip is used in order to inject the proper image name into the request to build a Docker container. Powerstrip, in turn, calls a small Sinatra Application which performs a lookup in Redis to find the proper name for the host’s architecture. If the image name is not registered with Redis, then it is passed through without modification. It can be configured to either provide the image name for every architecture of a canonical name, or such that multifarious replaces the default name only in the case of a “special case”.

Quite possibly a future version will be written in Go and rather than requiring multiple executables to perform the injection, I expect to merge powerstrip and the adapter into one. This should reduce the footprint a good deal.

I am still working on a cohesive demo, but the following will show that the dependency injection is working:

The -i is needed due to a powerstrip quirk. However, take note that the docker image being invoked on the command line is ‘hello’. The docker image being run is that of ‘hello-world’ and there is no ‘hello’ image. Injection is working and I can configure images to run based upon the architecture.

I’ve injected the proper name for the image based upon a Redis lookup. I chose Redis because it’s available for multiple platforms and is pretty easy to use. It just needs to have the lookup table fed to it.

The items are stored in Redis as a HSET:

At runtime the image is chosen and injected and life proceeds.

The repository is available on github and will be added to in the next couple of days, with a full-fledged writeup and demo to follow in the next couple of days.

The Feaured Image is a modification of a photo by JD Hancock:

flickr photo shared by JD Hancock under a Creative Commons ( BY ) license