Comment 0 for bug 1813703

[L2] [summary] ovs-agent issues at large scale

Recently we have tested the ovs-agent with ovs-flow based firewall, and we met some issues at large scale.
This bug will give us a centralized location to track the following problems.

Problems:
(1) RPC timeout during ovs-agent restart
(2) local connection to ovs-vswitchd was drop or timeout
(3) ovs-agent failed to restart
(4) ovs-agent restart costs too long time (15-40mins+)
(5) unexpected flow lost
(6) unexpected tunnel lost
(7) multipe cookies flows (stale flows)
(8) dump-flows takes a lots of time
(9) really hard to do trouble shooting if one VM lost the connection, flow tables are almost unreadable (reach 30k+ flows).

Problem can be seen in the following scenarios:
(1) 2000-3000 ports related to one single security group (or one remote security group)
(2) create 2000-3000 VMs in one single subnet (network)
(3) create 2000-3000 VMs under one single security group

Yes, the scale is the main problem, when one host's VM count is closing to 150-200 (at the same time the ports number in one subnet or security group is closing 2000), the ovs-agent restart will get worse.

Test ENV:
stable/queens

Deployment topology:
neutron-server, database, message queue all have its own dedicated physical hosts, 3 nodes for each service at least.

Configurations:
ovs-agent was setup with l2pop, firewall based on ovs flow, and the config was basiclly like the following:
[agent]
enable_distributed_routing = True
l2_population = True
tunnel_types = vxlan
arp_responder = True
prevent_arp_spoofing = True
extensions = qos
report_interval = 60

[ovs]
bridge_mappings = tenant:br-vlan,external:br-ex
local_ip = 10.114.4.48

[securitygroup]
firewall_driver = openvswitch
enable_security_group = True

Some issue tracking:
(1) mostly because the great number of ports related to one security grop or in one network
(2) uncessary RPC call during ovs-agent restart
(3) inefficient database query conditions
(4) full sync will redo again and again if any exception was raised in rpc_loop
(5) clean stale flows will dump all flows first (not once, multipe times), this is really time-consuming

So this is a summay bug for the entire scale issues we have met.

Some potential solutions:
Increase some config like rpc_response_timeout, of_connect_timeout, of_request_timeout, ovsdb_timeout etc,
does not help too much, and these changes can cause the restart cost time much more. And those issues can still be seen.

One workaround is to disable the openvswitch flow based security group, the ovs-agent can restart in less than 10 mins.