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Hello,

Lately, I've been working on a fix[1] for the amhpora-agent, which
currently only support Debian based flavors such as Ubuntu.

The main Issues here:
1. NIC hot plugs: Ubuntu's ethX.cfg files looks different from ifcfg-ethX
files which are accepted in Linux flavors such a RHEL, CentOS and Fedora,
read more in the fix commit msg.
2. The usage of Flavor specific features such as 'upstart'.

I would like to have a discussion about the second bullet mentioned above.
Due to the fact that in Octavia the loadbalancer runs inside of an instance
(Amphora), There are few actions that need to take place in the Amphora
instance boot process:
a. namespace and NIC created.
b. amphora agent starts
c. haproxy (and possibly keepalived) start

The Amphora-agent leverages[2] the capabilities of 'upstart' to make that
happen, which is a bit problematic if we wish it to work on other flavors.
The default cloud image for Amphora today is Ubuntu, yet there are few more
options[3] such as CentOS and Fedora.
Unlike the Ubuntu base image, which uses 'sysvinit', The latter two flavors
use 'systemd'.
This creates incompatibility with the jinja2[4][5] templates used by the
agent.

The way I see it there are two possible solutions for this:
1. Include a systemd equivalent in the fix[1] that will essentially
duplicate the functionality mentioned above and work in the other flavors.
2. Have a the amphora agent be the only binary that needs to be configured
to start upon boot, and that agent will take care of plugging namespaces
and NICs and also spawning needs processes. This is how it is done in lbaas
and l3 agents.

While the latter solution looks like a more "clean" design, the trade-off
here is a bigger change to the amphora agent.

[1] https://review.openstack.org/#/c/331841/
[2]
https://github.com/openstack/octavia/blob/master/octavia/amphorae/backends/agent/api_server/listener.py#L128
[3]
https://github.com/openstack/octavia/blob/master/diskimage-create/diskimage-create.sh#L27
[4]
https://github.com/openstack/octavia/blob/master/octavia/amphorae/backends/agent/api_server/templates/upstart.conf.j2
[5]
https://github.com/openstack/octavia/blob/master/octavia/amphorae/backends/agent/api_server/templates/sysvinit.conf.j2


Thanks,
Nir
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