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.
그 Dockerfile that builds arungupta/couchbase image is:
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FROM 카우치베이스:latest COPY configure–node.sh /opt/카우치베이스 HEALTHCHECK —interval=5s —시간 초과=3s CMD curl —fail https://localhost:8091/pools || exit 1 CMD [“/opt/couchbase/configure-node.sh”] |
It uses configure-node.sh script to configure the server using Couchbase REST API. The new instruction to notice here is HEALTHCHECK. This instruction can be specified as:
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HEALTHCHECK CMD |
그 can be:
--interval=DURATION(default 30s)--timeout=DURATION(default 30s)--retries=N(default 3)
그 is the command that runs inside the container to check it’s health. If health check is enabled, then the container can have three states:
starting– Initial status when the container is still startinghealthy– If the command succeeds then the container is healthy- unhealthy – If a single run of the
takes longer than the specified timeout then it is considered unhealthy. If a health check fails, retries will be run several times and the Docker container status will be declared unhealthy if it still fails.
The Docker commands exit status indicates the HEALTHCHECK status of the container. The following values are allowed:
0– container is healthy1– container is not healthy
In our instruction, /pools REST API is invoked using curl. If the command fails then an exit status of 1 is returned, and this marks the container unhealthy for that attempt. This Docker HEALTHCHECK command is invoked every 5 seconds. The container is marked unhealthy if the command does not return successfully within 3 seconds. Run the container as:
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docker run –d —name db arungupta/카우치베이스:latest |
Check Docker container status:
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docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 55b14302671e arungupta/카우치베이스:latest “/entrypoint.sh /opt/” 2 seconds ago Up 1 seconds (health: starting) 8091–8094/tcp, 11207/tcp, 11210–11211/tcp, 18091–18093/tcp db |
Notice how health: starting status is reported in the STATUS column. Checking after a few seconds shows the status:
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docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 55b14302671e arungupta/카우치베이스:latest “/entrypoint.sh /opt/” 소개 a minute ago Up 소개 a minute (healthy) 8091–8094/tcp, 11207/tcp, 11210–11211/tcp, 18091–18093/tcp db |
And now it’s reported healthy. More details about this HEALTHCHECK instruction can be found on docs.docker.com. Now, if you are running an image that does not have HEALTHCHECK instruction then the docker run command can be used to specify similar values. An equivalent runtime command would be:
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docker run –d —name db —health–cmd “curl –fail https://localhost:8091/pools || exit 1” —health–interval=5s —시간 초과=3s arungupta/카우치베이스 |
Last 5 health checks for a container can be obtained using the docker inspect command:
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docker inspect —format=‘{{json .State.Health}}’ db |
The output is shown as:
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{ “Status”: “healthy”, “FailingStreak”: 0, “Log”: [ { “Start”: “2016-11-12T03:23:03.351561Z”, “End”: “2016-11-12T03:23:03.422176171Z”, “ExitCode”: 0, “Output”: ” % Total % Received % Xferd Average Speed Time Time Time Currentn Dload Upload Total Spent Left Speednr 0 0 0 0 0 0 0 0 –:–:– –:–:– –:–:– 0r100 768 100 768 0 0 595k 0 –:–:– –:–:– –:–:– 750kn{“isAdminCreds“:true,”isROAdminCreds“:false,”isEnterprise“:true,”pools“:[{“name“:”기본값“,”uri“:”/pools/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“,”streamingUri“:”/poolsStreaming/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“}],”settings“:{“maxParallelIndexers“:”/settings/maxParallelIndexers?uuid=1b84cdbd136e4e8466049dd062dd6969“,”viewUpdateDaemon“:”/settings/viewUpdateDaemon?uuid=1b84cdbd136e4e8466049dd062dd6969“},”uuid“:”1b84cdbd136e4e8466049dd062dd6969“,”implementationVersion“:”4.5.1–2844–enterprise“,”componentsVersion“:{“lhttpc“:”1.3.0“,”os_mon“:”2.2.14“,”공공의_열쇠“:”0.21“,”asn1“:”2.0.4“,”kernel“:”2.16.4“,”ale“:”4.5.1–2844–enterprise“,”inets“:”5.9.8“,”ns_server“:”4.5.1–2844–enterprise“,”crypto“:”3.2“,”ssl“:”5.3.3“,”sasl“:”2.3.4“,”stdlib“:”1.19.4“}}” }, { “Start”: “2016-11-12T03:23:08.423558928Z”, “End”: “2016-11-12T03:23:08.510122392Z”, “ExitCode”: 0, “Output”: ” % Total % Received % Xferd Average Speed Time Time Time Currentn Dload Upload Total Spent Left Speednr 0 0 0 0 0 0 0 0 –:–:– –:–:– –:–:– 0r100 768 100 768 0 0 309k 0 –:–:– –:–:– –:–:– 375kn{“isAdminCreds“:true,”isROAdminCreds“:false,”isEnterprise“:true,”pools“:[{“name“:”기본값“,”uri“:”/pools/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“,”streamingUri“:”/poolsStreaming/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“}],”settings“:{“maxParallelIndexers“:”/settings/maxParallelIndexers?uuid=1b84cdbd136e4e8466049dd062dd6969“,”viewUpdateDaemon“:”/settings/viewUpdateDaemon?uuid=1b84cdbd136e4e8466049dd062dd6969“},”uuid“:”1b84cdbd136e4e8466049dd062dd6969“,”implementationVersion“:”4.5.1–2844–enterprise“,”componentsVersion“:{“lhttpc“:”1.3.0“,”os_mon“:”2.2.14“,”공공의_열쇠“:”0.21“,”asn1“:”2.0.4“,”kernel“:”2.16.4“,”ale“:”4.5.1–2844–enterprise“,”inets“:”5.9.8“,”ns_server“:”4.5.1–2844–enterprise“,”crypto“:”3.2“,”ssl“:”5.3.3“,”sasl“:”2.3.4“,”stdlib“:”1.19.4“}}” }, { “Start”: “2016-11-12T03:23:13.511446818Z”, “End”: “2016-11-12T03:23:13.58141325Z”, “ExitCode”: 0, “Output”: ” {“isAdminCreds“:true,”isROAdminCreds“:false,”isEnterprise“:true,”pools“:[{“name“:”기본값“,”uri“:”/pools/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“,”streamingUri“:”/poolsStreaming/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“}],”settings“:{“maxParallelIndexers“:”/settings/maxParallelIndexers?uuid=1b84cdbd136e4e8466049dd062dd6969“,”viewUpdateDaemon“:”/settings/viewUpdateDaemon?uuid=1b84cdbd136e4e8466049dd062dd6969“},”uuid“:”1b84cdbd136e4e8466049dd062dd6969“,”implementationVersion“:”4.5.1–2844–enterprise“,”componentsVersion“:{“lhttpc“:”1.3.0“,”os_mon“:”2.2.14“,”공공의_열쇠“:”0.21“,”asn1“:”2.0.4“,”kernel“:”2.16.4“,”ale“:”4.5.1–2844–enterprise“,”inets“:”5.9.8“,”ns_server“:”4.5.1–2844–enterprise“,”crypto“:”3.2“,”ssl“:”5.3.3“,”sasl“:”2.3.4“,”stdlib“:”1.19.4“}} % Total % Received % Xferd Average Speed Time Time Time Currentn Dload Upload Total Spent Left Speednr 0 0 0 0 0 0 0 0 –:–:– –:–:– –:–:– 0r100 768 100 768 0 0 248k 0 –:–:– –:–:– –:–:– 375kn” }, { “Start”: “2016-11-12T03:23:18.583512367Z”, “End”: “2016-11-12T03:23:18.677727356Z”, “ExitCode”: 0, “Output”: ” % Total % Received % Xferd Average Speed Time Time Time Currentn Dlo{“isAdminCreds“:true,”isROAdminCreds“:false,”isEnterprise“:true,”pools“:[{“name“:”기본값“,”uri“:”/pools/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“,”streamingUri“:”/poolsStreaming/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“}],”settings“:{“maxParallelIndexers“:”/settings/maxParallelIndexers?uuid=1b84cdbd136e4e8466049dd062dd6969“,”viewUpdateDaemon“:”/settings/viewUpdateDaemon?uuid=1b84cdbd136e4e8466049dd062dd6969“},”uuid“:”1b84cdbd136e4e8466049dd062dd6969“,”implementationVersion“:”4.5.1–2844–enterprise“,”componentsVersion“:{“lhttpc“:”1.3.0“,”os_mon“:”2.2.14“,”공공의_열쇠“:”0.21“,”asn1“:”2.0.4“,”kernel“:”2.16.4“,”ale“:”4.5.1–2844–enterprise“,”inets“:”5.9.8“,”ns_server“:”4.5.1–2844–enterprise“,”crypto“:”3.2“,”ssl“:”5.3.3“,”sasl“:”2.3.4“,”stdlib“:”1.19.4“}}ad Upload Total Spent Left Speednr 0 0 0 0 0 0 0 0 –:–:– –:–:– –:–:– 0r100 768 100 768 0 0 307k 0 –:–:– –:–:– –:–:– 375kn” }, { “Start”: “2016-11-12T03:23:23.679661467Z”, “End”: “2016-11-12T03:23:23.782372291Z”, “ExitCode”: 0, “Output”: ” % Total % Received % Xferd Average Speed Time Time Time Currentn Dload Upload Total Spent Left{“isAdminCreds“:true,”isROAdminCreds“:false,”isEnterprise“:true,”pools“:[{“name“:”기본값“,”uri“:”/pools/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“,”streamingUri“:”/poolsStreaming/기본값?uuid=1b84cdbd136e4e8466049dd062dd6969“}],”settings“:{“maxParallelIndexers“:”/settings/maxParallelIndexers?uuid=1b84cdbd136e4e8466049dd062dd6969“,”viewUpdateDaemon“:”/settings/viewUpdateDaemon?uuid=1b84cdbd136e4e8466049dd062dd6969“},”uuid“:”1b84cdbd136e4e8466049dd062dd6969“,”implementationVersion“:”4.5.1–2844–enterprise“,”componentsVersion“:{“lhttpc“:”1.3.0“,”os_mon“:”2.2.14“,”공공의_열쇠“:”0.21“,”asn1“:”2.0.4“,”kernel“:”2.16.4“,”ale“:”4.5.1–2844–enterprise“,”inets“:”5.9.8“,”ns_server“:”4.5.1–2844–enterprise“,”crypto“:”3.2“,”ssl“:”5.3.3“,”sasl“:”2.3.4“,”stdlib“:”1.19.4“}} Speednr 0 0 0 0 0 0 0 0 –:–:– –:–:– –:–:– 0r100 768 100 768 0 0 439k 0 –:–:– –:–:– –:–:– 750kn” } ] } |
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