first commit

Dockerfile

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+FROM nginx:alpine
+
+RUN apk --update add curl
+
+HEALTHCHECK \
+  --interval=2s \
+  --timeout=2s \
+  --retries=2 \
+  CMD curl -s http://localhost/status | grep -q '^alive$'
+
+COPY entrypoint.sh /entrypoint.sh
+ENTRYPOINT ["sh", "/entrypoint.sh"]

README.md

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+## Docker Swarm health check example
+
+This example shows how health check works in Docker Swarm.
+
+### What does this container do?
+
+Container runs a nginx server and it also runs a script which writes a ``dead``
+status to ``/usr/share/nginx/html/status`` file on every odd run which is then
+picked by the health check that expects ``alive`` status from the nginx running
+in the container.
+
+So every odd run the container gets ``unhealthy`` status.
+Then you can observe that running this container in Docker Engine alone will
+not restart it. Hence we will run it as a service in the Docker Swarm which
+will ensure the container gets restarted until it gets ``healthy`` status.
+
+### Building image
+
+```
+docker build -t healthcheck-test .
+```
+
+### Setting up env
+
+Make sure you have recent Docker Engine installed.
+
+```
+docker swarm init
+```
+
+### Running the service
+
+```
+docker service create \
+  --name test1 \
+  --mount type=bind,src=/tmp,dst=/usr/share/nginx/html \
+  --detach healtcheck-test
+```
+
+### Watching the healtcheck
+
+```
+docker ps |grep test1
+docker service ls
+```
+
+### Cleaning up
+
+```
+docker service rm test1
+docker swarm leave --force
+rm -rf -- /tmp/html
+```
+
+### Extra
+
+If you want to restart the container manually, you need to downscale it to 0
+first and then upscale it back again.
+
+```
+docker service scale test1=0
+docker service scale test1=1
+```
+
+### References
+
+- https://docs.docker.com/compose/compose-file/
+- https://docs.docker.com/engine/reference/builder/

entrypoint.sh

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+#!/bin/sh
+
+# Mount /usr/share/nginx/html must be persistent for this test to work properly
+# in the Docker Swarm since it does not just restart the container but rather
+# removes it and then starts it.
+SFILE=/usr/share/nginx/html/status
+
+# I am unhealthy until I get restarted and then I will become healthy again.
+# That way I will be healthy every even run and unhealthy every odd run.
+grep dead $SFILE && ( echo alive | tee $SFILE ) || ( echo dead | tee $SFILE )
+
+exec nginx -g "daemon off;"