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mention health check in docs

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Daniel Barlow 2024-07-30 22:53:21 +01:00
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doc/configuration.rst
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@ -83,22 +83,28 @@ service supervisor. A typical SOHO router might have services to
* enable/disable IP packet forwarding
* mount filesystems
(Some of these might not be considered services using other definitions
of the term: for example, this use of L2TP would be a "client" in the
client/server classification; and enabling packet forwarding doesn't
require any long-lived process - just a setting to be toggled.
However, there is value in being able to use the same abstractions for
all the things to manage them and specify their dependency
relationships - so in Liminix "everything is a service")
(Some of these might not be considered services using other
definitions of the term: for example, this L2TP process would be a
"client" in the client/server classification; and enabling packet
forwarding doesn't require any long-lived process - just a setting to
be toggled. However, there is value in being able to use the same
abstractions for all the things to manage them and specify their
dependency relationships - so in Liminix "everything is a service")
The service supervision system enables service health monitoring,
restart of unhealthy services, and failover to "backup" services when
a primary service fails or its dependencies are unavailable. The
intention is that you have a framework in which you can specify policy
requirements like "ethernet wan dhcp-client should be restarted if it
crashes, but if it can't start because the hardware link is down, then
4G ppp service should be started instead".
Any attribute in `config.services` will become part of the default set
of services that s6-rc will try to bring up.
Services are usually started at boot time, but **controlled services**
are those that are required only in particular contexts. For example,
a service to mount a USB backup drive should run only when the drive
is attached to the system. Liminix currently implements two kinds of
controlled service:
of services that s6-rc will try to bring up. Services are usually
started at boot time, but **controlled services** are those that are
required only in particular contexts. For example, a service to mount
a USB backup drive should run only when the drive is attached to the
system. Liminix currently implements three kinds of controlled service:
* "uevent-rule" service controllers use sysfs/uevent to identify when
particular hardware devices are present, and start/stop a controlled
@ -108,6 +114,10 @@ controlled service:
it allows you to specify a list of services and runs each of them
in turn until it exits, then runs the next.
* the "health-check" service wraps another service, and runs a "health
check" command at regular intervals. When the health check fails,
indicating that the wrapped service is not working, it is terminated
and allowed to restart
Writing services