One of the new features in Docker 1.12 is how health check for a container can be baked into the image definition. And this can be overridden at the command line.
Just like the CMD instruction, there can be multiple HEALTHCHECK instructions in Dockerfile but only the last one is effective.
This is a great addition because a container reporting status as Up 1 hour may return errors. The container may be up but there is no way for the application inside the container to provide a status. This instruction fixes that.
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