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>
A previous change added a TTY fixup for stdin on older Windows versions to
work around a Windows issue with backspace/delete behavior. This change
used the OS version to determine whether to activate the behavior.
However, the Windows bug is actually in the image, not the OS, so it
should have used the image's OS version.
This ensures that a Server TP5 container running on Windows 10 will have
reasonable console behavior.
Signed-off-by: John Starks <jostarks@microsoft.com>
In Windows containers in TP5, DEL is interpreted as the delete key, but
Linux generally interprets it as backspace. This prevents backspace from
working when using a Linux terminal or the native console terminal
emulation in Windows.
To work around this, translate DEL to BS in Windows containers stdin when
TTY is enabled. Do this only for builds that do not have the fix in
Windows itself.
Signed-off-by: John Starks <jostarks@microsoft.com>
Removing the call to Shutdown from within Signal in order to rely on waitExit handling the exit of the process.
Signed-off-by: Stefan J. Wernli <swernli@microsoft.com>
This change enables the workflow of finishing installing Windows OS updates in the container after it has completed running, via a special servicing container.
Signed-off-by: Stefan J. Wernli <swernli@microsoft.com>
Signed-off-by: John Howard <jhoward@microsoft.com>
Signed-off-by: John Starks <jostarks@microsoft.com>
Signed-off-by: Darren Stahl <darst@microsoft.com>
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
