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This PR adds support for user-defined health-check probes for Docker
containers. It adds a `HEALTHCHECK` instruction to the Dockerfile syntax plus
some corresponding "docker run" options. It can be used with a restart policy
to automatically restart a container if the check fails.
The `HEALTHCHECK` instruction has two forms:
* `HEALTHCHECK [OPTIONS] CMD command` (check container health by running a command inside the container)
* `HEALTHCHECK NONE` (disable any healthcheck inherited from the base image)
The `HEALTHCHECK` instruction tells Docker how to test a container to check that
it is still working. This can detect cases such as a web server that is stuck in
an infinite loop and unable to handle new connections, even though the server
process is still running.
When a container has a healthcheck specified, it has a _health status_ in
addition to its normal status. This status is initially `starting`. Whenever a
health check passes, it becomes `healthy` (whatever state it was previously in).
After a certain number of consecutive failures, it becomes `unhealthy`.
The options that can appear before `CMD` are:
* `--interval=DURATION` (default: `30s`)
* `--timeout=DURATION` (default: `30s`)
* `--retries=N` (default: `1`)
The health check will first run **interval** seconds after the container is
started, and then again **interval** seconds after each previous check completes.
If a single run of the check takes longer than **timeout** seconds then the check
is considered to have failed.
It takes **retries** consecutive failures of the health check for the container
to be considered `unhealthy`.
There can only be one `HEALTHCHECK` instruction in a Dockerfile. If you list
more than one then only the last `HEALTHCHECK` will take effect.
The command after the `CMD` keyword can be either a shell command (e.g. `HEALTHCHECK
CMD /bin/check-running`) or an _exec_ array (as with other Dockerfile commands;
see e.g. `ENTRYPOINT` for details).
The command's exit status indicates the health status of the container.
The possible values are:
- 0: success - the container is healthy and ready for use
- 1: unhealthy - the container is not working correctly
- 2: starting - the container is not ready for use yet, but is working correctly
If the probe returns 2 ("starting") when the container has already moved out of the
"starting" state then it is treated as "unhealthy" instead.
For example, to check every five minutes or so that a web-server is able to
serve the site's main page within three seconds:
HEALTHCHECK --interval=5m --timeout=3s \
CMD curl -f http://localhost/ || exit 1
To help debug failing probes, any output text (UTF-8 encoded) that the command writes
on stdout or stderr will be stored in the health status and can be queried with
`docker inspect`. Such output should be kept short (only the first 4096 bytes
are stored currently).
When the health status of a container changes, a `health_status` event is
generated with the new status. The health status is also displayed in the
`docker ps` output.
Signed-off-by: Thomas Leonard <thomas.leonard@docker.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
49 lines
1.3 KiB
Go
49 lines
1.3 KiB
Go
package container
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import (
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"github.com/Sirupsen/logrus"
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"github.com/docker/engine-api/types"
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)
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// Health holds the current container health-check state
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type Health struct {
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types.Health
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stop chan struct{} // Write struct{} to stop the monitor
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}
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// String returns a human-readable description of the health-check state
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func (s *Health) String() string {
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if s.stop == nil {
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return "no healthcheck"
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}
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switch s.Status {
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case types.Starting:
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return "health: starting"
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default: // Healthy and Unhealthy are clear on their own
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return s.Status
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}
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}
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// OpenMonitorChannel creates and returns a new monitor channel. If there already is one,
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// it returns nil.
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func (s *Health) OpenMonitorChannel() chan struct{} {
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if s.stop == nil {
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logrus.Debugf("OpenMonitorChannel")
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s.stop = make(chan struct{})
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return s.stop
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}
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return nil
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}
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// CloseMonitorChannel closes any existing monitor channel.
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func (s *Health) CloseMonitorChannel() {
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if s.stop != nil {
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logrus.Debugf("CloseMonitorChannel: waiting for probe to stop")
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// This channel does not buffer. Once the write succeeds, the monitor
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// has read the stop request and will not make any further updates
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// to c.State.Health.
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s.stop <- struct{}{}
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s.stop = nil
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logrus.Debugf("CloseMonitorChannel done")
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}
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}
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