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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>
61 lines
1.9 KiB
Go
61 lines
1.9 KiB
Go
package libcontainerd
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import "io"
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// State constants used in state change reporting.
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const (
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StateStart = "start-container"
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StatePause = "pause"
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StateResume = "resume"
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StateExit = "exit"
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StateRestart = "restart"
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StateRestore = "restore"
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StateStartProcess = "start-process"
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StateExitProcess = "exit-process"
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StateOOM = "oom" // fake state
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stateLive = "live"
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)
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// CommonStateInfo contains the state info common to all platforms.
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type CommonStateInfo struct { // FIXME: event?
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State string
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Pid uint32
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ExitCode uint32
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ProcessID string
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}
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// Backend defines callbacks that the client of the library needs to implement.
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type Backend interface {
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StateChanged(containerID string, state StateInfo) error
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AttachStreams(processFriendlyName string, io IOPipe) error
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}
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// Client provides access to containerd features.
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type Client interface {
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Create(containerID string, spec Spec, options ...CreateOption) error
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Signal(containerID string, sig int) error
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SignalProcess(containerID string, processFriendlyName string, sig int) error
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AddProcess(containerID, processFriendlyName string, process Process) error
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Resize(containerID, processFriendlyName string, width, height int) error
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Pause(containerID string) error
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Resume(containerID string) error
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Restore(containerID string, options ...CreateOption) error
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Stats(containerID string) (*Stats, error)
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GetPidsForContainer(containerID string) ([]int, error)
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Summary(containerID string) ([]Summary, error)
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UpdateResources(containerID string, resources Resources) error
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}
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// CreateOption allows to configure parameters of container creation.
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type CreateOption interface {
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Apply(interface{}) error
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}
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// IOPipe contains the stdio streams.
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type IOPipe struct {
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Stdin io.WriteCloser
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Stdout io.Reader
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Stderr io.Reader
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Terminal bool // Whether stderr is connected on Windows
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}
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