Fix systemd startup

[jreidinger]

Problem

Problem description is in issue #1539

Solution

Implement sd_notify for agama-web-service to notify systemd when web service is ready to serve requests.
Improve systemd dependencies to better reflect dependencies. For agama-auto adapt dependencies to reflect that CLI switch from direct systemd communication to HTTP API. related PR is #1438

Testing

• Tested manually

Screenshots

snippet from log before change ( truncated, but to demonstrate that agama-auto runs too soon):

Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Started Agama Installer Service.
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Started Agama Web Server.
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Started Agama automatic profile runner.
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Starting Postpone login prompt after the SSL fingerprint issue is generated...
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + export YAST_SKIP_XML_VALIDATION=1
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + YAST_SKIP_XML_VALIDATION=1
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + '[' -z '' ']'
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2691]: ++ awk -F agama.auto= '{sub(/ .*$/, "", $2); print $2}'
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + url=
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + '[' -z '' ']'
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + echo 'no autoinstallation profile'
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: no autoinstallation profile
Aug 14 13:10:47 dhcp118.suse.cz agama-auto[2689]: + exit 0
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: agama-auto.service: Deactivated successfully.
Aug 14 13:10:47 dhcp118.suse.cz sshd-gen-keys-start[2683]: ssh-keygen: generating new host keys: RSA ECDSA ED25519
Aug 14 13:10:47 dhcp118.suse.cz sshd[2702]: Server listening on 0.0.0.0 port 22.
Aug 14 13:10:47 dhcp118.suse.cz sshd[2702]: Server listening on :: port 22.
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Started OpenSSH Daemon.
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Starting Generate issue file for SSH host keys...
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: agama-ssh-issue.service: Deactivated successfully.
Aug 14 13:10:47 dhcp118.suse.cz systemd[1]: Finished Generate issue file for SSH host keys.
Aug 14 13:10:47 dhcp118.suse.cz agama-web-server[2688]: registering event source with poller: token=Token(94923250365696), interests=READABLE | WRITABLE
Aug 14 13:10:47 dhcp118.suse.cz agama-web-server[2688]: Initializing
Aug 14 13:10:47 dhcp118.suse.cz agama-web-server[2688]: Waiting for DATA or OK from server
Aug 14 13:10:47 dhcp118.suse.cz agama-web-server[2688]: Received OK from server
Aug 14 13:10:47 dhcp118.suse.cz agama-web-server[2688]: Waiting for Unix FD passing agreement from server
Aug 14 13:10:47 dhcp118.suse.cz agama-web-server[2688]: Unix FD passing agreed by server

and now after change:

Aug 15 10:19:15 dhcp118.suse.cz systemd[1]: Started Agama Web Server.
Aug 15 10:19:15 dhcp118.suse.cz agama-web-server[12467]: Starting Agama web server at :::80
Aug 15 10:19:15 dhcp118.suse.cz agama-web-server[12467]: Starting Agama web server at :::443
...
Aug 15 10:19:15 dhcp118.suse.cz agama-web-server[12467]: Waiting for message on the socket..
...
Aug 15 10:19:15 dhcp118.suse.cz agama-web-server[12467]: Listening for property changes on org.freedesktop.NetworkManager.Device...
Aug 15 10:19:15 dhcp118.suse.cz systemd[1]: Started Agama automatic profile runner.
Aug 15 10:19:15 dhcp118.suse.cz agama-web-server[12467]: Message received on the socket: Msg { type: Signal, sender: UniqueName(Str(Borrowed(":1.2"))), path: ObjectPath("/org/freedesktop/systemd1/unit/agama_2dauto_2eservice"), iface: InterfaceName(Str(Borrowed("org.freedesktop.DBus.Properties"))), member: MemberName(Str(Borrowed("PropertiesChanged"))), body: Signature("sa{sv}as") }
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + export YAST_SKIP_XML_VALIDATION=1
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + YAST_SKIP_XML_VALIDATION=1
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + '[' -z '' ']'
...
Aug 15 10:19:15 dhcp118.suse.cz agama-web-server[12467]: Waiting for message on the socket..
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12482]: ++ awk -F agama.auto= '{sub(/ .*$/, "", $2); print $2}'
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + url=
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + '[' -z '' ']'
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + echo 'no autoinstallation profile'
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: no autoinstallation profile
Aug 15 10:19:15 dhcp118.suse.cz agama-auto[12479]: + exit 0
Aug 15 10:19:15 dhcp118.suse.cz systemd[1]: agama-auto.service: Deactivated successfully.

[mchf]

lgtm

[mvidner]

Nice :)
A funny thing, this manual page contains also the implementation of the notification mechanism, in C and Python: https://www.man7.org/linux/man-pages/man3/sd_notify.3.html