How to group / compose systemd services

systemd

I have three systemd services (Docker containers, but that is not important). All three of these services has to be running for the application to be fully functional.

In order to simplify procedures for the ops team I've created a forth systemd service to group them all together using the Requires and PartOf directives. Starting and stopping this forth service will now start and stop the three containers in the correct order.

The last challenge is to get the forth systemd service to show the correct status. Right now it shows "loaded / inactive" after booting up the services. Is it possible to configure it in a way that it will show "loaded / active" when and only when the three first services are up and running?

[Unit]
Description=This is the group
Requires=a.service b.service c.service

[Service]
ExecStart=/bin/echo "Starting"
ExecStop=/bin/echo "Stopping"

[Install]
WantedBy=local.target

The a.service, b.service and c.service contains PartOf=group.service

Best Answer

I think you need to add an After= clause. If your three services are linked, you might also be able to simplify your Requires.

If you also wanted this fourth service to stop when the other 3 do, you would also need to add a BindsTo entry.

As in:

[Unit]
Description=This is the group
Requires=c.service
After=c.service
BindsTo=c.service

Related Solutions

Linux – way to control two instantiated systemd services as a single unit

Look at using the BindsTo option to tie the units together. The systemd.unit(5) manual page describes it like this:

BindsTo=

Configures requirement dependencies, very similar in style to Requires=, however in addition to this behavior, it also declares that this unit is stopped when any of the units listed suddenly disappears. Units can suddenly, unexpectedly disappear if a service terminates on its own choice, a device is unplugged or a mount point unmounted without involvement of systemd.

Which sounds like it should do what you want and tie one unit to the other so that whenever the master stops the slave stops as well and vice versa for starting up.

Don't forget that you can also use Before/After to specify the order in which they should start if necessary.

How to set environment variable in systemd service

Times change and so do best practices.

The current best way to do this is to run systemctl edit myservice, which will create an override file for you or let you edit an existing one.

In normal installations this will create a directory /etc/systemd/system/myservice.service.d, and inside that directory create a file whose name ends in .conf (typically, override.conf), and in this file you can add to or override any part of the unit shipped by the distribution.

For instance, in a file /etc/systemd/system/myservice.service.d/myenv.conf:

[Service]
Environment="SECRET=pGNqduRFkB4K9C2vijOmUDa2kPtUhArN"
Environment="ANOTHER_SECRET=JP8YLOc2bsNlrGuD6LVTq7L36obpjzxd"

Also note that if the directory exists and is empty, your service will be disabled! If you don't intend to put something in the directory, ensure that it does not exist.

For reference, the old way was:

The recommended way to do this is to create a file /etc/sysconfig/myservice which contains your variables, and then load them with EnvironmentFile.

For complete details, see Fedora's documentation on how to write a systemd script.

Best Answer

Related Solutions

Linux – way to control two instantiated systemd services as a single unit

How to set environment variable in systemd service

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