Design doc for clustering.

This is related to #2303 and steals from #2435.

docs/design/clustering/.gitignore

@@ -0,0 +1 @@
+DroidSansMono.ttf

docs/design/clustering/Makefile

@@ -0,0 +1,16 @@
+FONT := DroidSansMono.ttf
+
+PNGS := $(patsubst %.seqdiag,%.png,$(wildcard *.seqdiag))
+
+.PHONY: all
+all: $(PNGS)
+
+.PHONY: watch
+watch:
+	fswatch *.seqdiag | xargs -n 1 sh -c "make || true"
+
+$(FONT):
+	curl -sLo $@ https://googlefontdirectory.googlecode.com/hg/apache/droidsansmono/DroidSansMono.ttf
+
+%.png: %.seqdiag $(FONT)
+	seqdiag -a -f '$(FONT)' $<

docs/design/clustering/README.md

@@ -0,0 +1,9 @@
+This directory contains diagrams for the clustering design doc.
+
+This depends on the `seqdiag` [utility](http://blockdiag.com/en/seqdiag/index.html).  Assuming you have a non-borked python install, this should be installable with
+
+```bash
+pip install seqdiag
+```
+
+Just call `make` to regenerate the diagrams.

docs/design/clustering/dynamic.seqdiag

@@ -0,0 +1,24 @@
+seqdiag {
+  activation = none;
+
+
+  user[label = "Admin User"];
+  bootstrap[label = "Bootstrap API\nEndpoint"];
+  master;
+  kubelet[stacked];
+
+  user -> bootstrap [label="createCluster", return="cluster ID"];
+  user <-- bootstrap [label="returns\n- bootstrap-cluster-uri"];
+
+  user ->> master [label="start\n- bootstrap-cluster-uri"];
+  master => bootstrap [label="setMaster\n- master-location\n- master-ca"];
+
+  user ->> kubelet [label="start\n- bootstrap-cluster-uri"];
+  kubelet => bootstrap [label="get-master", return="returns\n- master-location\n- master-ca"];
+  kubelet ->> master [label="signCert\n- unsigned-kubelet-cert", return="retuns\n- kubelet-cert"];
+  user => master [label="getSignRequests"];
+  user => master [label="approveSignRequests"];
+  kubelet <<-- master [label="returns\n- kubelet-cert"];
+
+  kubelet => master [label="register\n- kubelet-location"]
+}

docs/design/clustering/static.seqdiag

@@ -0,0 +1,16 @@
+seqdiag {
+  activation = none;
+
+  admin[label = "Manual Admin"];
+  ca[label = "Manual CA"]
+  master;
+  kubelet[stacked];
+
+  admin => ca [label="create\n- master-cert"];
+  admin ->> master [label="start\n- ca-root\n- master-cert"];
+
+  admin => ca [label="create\n- kubelet-cert"];
+  admin ->> kubelet [label="start\n- ca-root\n- kubelet-cert\n- master-location"];
+
+  kubelet => master [label="register\n- kubelet-location"];
+}