Add health check to collator

README.md

@@ -84,3 +84,11 @@ $ pjs query.parachains.heads 100
   "heads": "0xe1efbf8cc2e1304da927986f4cd6964ce0888ce3995948bf71fe427b1a9d39b02101d2dac9c5342d7e8c4f4de2f5277ef860b3a518c1cd823b9a8cee175dce11bf7f57c5016e8a60a6cec16244b2cbf81a67a1dc7a825c288fc694997bc70e2d456400"
 }
 ```
+
+The collator includes its own health check, which you can inspect with
+
+```sh
+docker inspect --format='{{json .State.Health}}' cumulus_collator_1
+```
+
+The check runs every 5 minutes, and takes about a minute to complete each time. Most of that time is spent sleeping; it remains a very lightweight process.

docker/test-parachain-collator.dockerfile

@@ -37,11 +37,18 @@ RUN time cargo build --release -p cumulus-test-parachain-collator
 FROM debian:buster-slim as collator
 RUN apt-get update && apt-get install jq curl bash -y && \
     curl -sSo /wait-for-it.sh https://raw.githubusercontent.com/vishnubob/wait-for-it/master/wait-for-it.sh && \
-    chmod +x /wait-for-it.sh
+    chmod +x /wait-for-it.sh && \
+    curl -sL https://deb.nodesource.com/setup_12.x | bash - && \
+    apt-get install -y nodejs && \
+    npm install --global yarn && \
+    yarn global add @polkadot/[email protected]
 COPY --from=builder \
     /paritytech/cumulus/target/release/cumulus-test-parachain-collator /usr/bin
 COPY ./scripts/inject_bootnodes.sh /usr/bin
 CMD ["/usr/bin/inject_bootnodes.sh"]
+COPY ./scripts/healthcheck.sh /usr/bin/
+HEALTHCHECK --interval=300s --timeout=75s --start-period=30s --retries=3 \
+    CMD ["/usr/bin/healthcheck.sh"]
 
 # the runtime stage is normally built once, cached, and ignored, but can be
 # specified with the --target build flag. This just preserves one of the builder's
@@ -52,7 +59,6 @@ COPY --from=builder \
     /var/opt/
 CMD ["cp", "-v", "/var/opt/cumulus_test_parachain_runtime.compact.wasm", "/runtime/"]
 
-
 FROM debian:buster-slim
 COPY --from=builder \
     /paritytech/cumulus/target/release/cumulus-test-parachain-collator /usr/bin

scripts/healthcheck.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+set -e
+
+head () {
+    polkadot-js-api --ws ws://172.28.1.1:9944 query.parachains.heads 100 |\
+        jq -r .heads
+}
+
+start=$(head)
+sleep 60
+end=$(head)
+
+[ "$start" != "$end" ]