Add Dockerfile for sequence diagram generation

docs/design/clustering/Dockerfile

@@ -0,0 +1,12 @@
+FROM debian:jessie
+
+RUN apt-get update
+RUN apt-get -qy install python-seqdiag make curl
+
+WORKDIR /diagrams
+
+RUN curl -sLo DroidSansMono.ttf https://googlefontdirectory.googlecode.com/hg/apache/droidsansmono/DroidSansMono.ttf
+
+ADD . /diagrams
+
+CMD bash -c 'make >/dev/stderr && tar cf - *.png'

docs/design/clustering/Makefile

@@ -14,3 +14,16 @@ $(FONT):
 
 %.png: %.seqdiag $(FONT)
 	seqdiag --no-transparency -a -f '$(FONT)' $<
+
+# Build the stuff via a docker image
+.PHONY: docker
+docker:
+	docker build -t clustering-seqdiag .
+	docker run --rm clustering-seqdiag | tar xvf -
+
+docker-clean:
+	docker rmi clustering-seqdiag || true
+	docker images -q --filter "dangling=true" | xargs docker rmi
+
+fix-clock-skew:
+	boot2docker ssh sudo date -u -D "%Y%m%d%H%M.%S" --set "$(shell date -u +%Y%m%d%H%M.%S)"

docs/design/clustering/README.md

@@ -7,3 +7,20 @@ pip install seqdiag
 ```
 
 Just call `make` to regenerate the diagrams.
+
+## Building with Docker
+If you are on a Mac or your pip install is messed up, you can easily build with docker.
+
+```
+make docker
+```
+
+The first run will be slow but things should be fast after that.
+
+To clean up the docker containers that are created (and other cruft that is left around) you can run `make docker-clean`.
+
+If you are using boot2docker and get warnings about clock skew (or if things aren't building for some reason) then you can fix that up with `make fix-clock-skew`.
+
+## Automatically rebuild on file changes
+
+If you have the fswatch utility installed, you can have it monitor the file system and automatically rebuild when files have changed.  Just do a `make watch`.