2c1a2ed225
5 min was copy/paste from official docs. After reading more about health checks in real world usage most examples was using duration around 5 seconds for interval. By default docker will show if service is unhealthy after 3 intervals return error. So in previous timing service would be taken out of poll (by e.g. docker swarm) after 15 min. For all this time it would be returning errors for any communication to it. Now it will be removed from poll of running services after 15 seconds. Regarding timeout more examples was using something shorter. For all services we are using if anything respond longer than 2 seconds then something is wrong with this service. Monasca is not web service but back-end service that should have high throughput. Change-Id: I4486c4974de38dea33739fdc470f38fd99d428fa
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Docker base image for Monasca services
This image is used as a starting point for images of all Monasca services.
Building monasca-base image
You need to have Docker installed (minimum tested version is
17.09). Then you can build image inside of this folder by
running:
docker build --no-cache -t monasca-base:1.0.0 .
Building child image
In the example folder you can find samples of how to
start building new child image using monasca-base.
Requirements
Every child image has to provide two files:
- start.sh
-
In this starting script provide all steps that lead to the proper service start. Including usage of wait scripts and templating of configuration files. You also could provide the ability to allow running container after service died for easier debugging.
- health_check.py
-
This file will be used for checking the status of the application running in the container. It should be used to inform Docker that service is operating and healthy. It will be useful for container orchestration like Kubernetes or Docker Swarm to properly handle services that are still running but stopped being responsive. Avoid using curl directly and instead, use health_check.py written with specific service in mind. It will provide more flexibility like when creating JSON request body.
Wait scripts
Some Python libraries are already pre-installed: pykafka and PyMySQL. They are used by wait scripts and in the process of creating the child image pip3 will reinstall them to use proper versions confronting the upper constraints file.
These wait scripts will be available in every child image and can be used in start.sh to avoid unnecessary errors and restarts of containers when they are started.
python3 /kafka_wait_for_topics.py || exit 1
python3 /mysql_check.py || exit 1
/wait_for.sh 192.168.10.6:5000 || exit 1Please, check the content of each of these files for documentation of what environment variables are used and more usage examples.
Useful commands
List all labels of the image (you need to have jq
installed):
docker inspect monasca-api:master | jq .[].Config.Labels
Get all steps of the Docker image build process history:
docker history --no-trunc <IMAGE_ID>
docker history --no-trunc monasca-base:1.0.0