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RUN apk --update add curl
CMD curl -s http://localhost/status | grep -q '^alive$'
COPY entrypoint.sh /entrypoint.sh
ENTRYPOINT ["sh", "/entrypoint.sh"]
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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 \
### Watching the healtcheck
docker ps |grep test1
docker service ls
### Cleaning up
docker service rm test1
docker swarm leave --force
rm -rf -- /tmp/html
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
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# 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.
# 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;"