Generated amphora images don't support UDP load balancing

Subscribing field medium since we have a test amphora that works but this is just a temporary fix.

I realize that I didn't specifically mention that the amphora that doesn't work was created by the octavia-diskimage-retrofit charm based on ubuntu images synced using glance-simiplestreams-sync. I tried with both bionic and focal based images.

haproxy does not support UDP load-balancing
https://github.com/haproxy/haproxy/issues/62

I think we need images that support the use of LVS & keepalived to do that (I would expect that keepalived and ipvsadm need to be installed):

https://storyboard.openstack.org/#!/story/1657091
https://github.com/openstack/octavia/tree/stable/train/octavia/common/jinja/lvs

I am going to check if anything is missing in order to make it work.

Sources of elements for disk image builder (dib):

https://github.com/openstack-charmers/octavia-diskimage-retrofit/tree/master/src/elements (openstack-charmers-specific elements shipped with the snap)
https://github.com/openstack/diskimage-builder/tree/master/diskimage_builder/elements (disk-image-builder-specific)
https://github.com/openstack/octavia/tree/master/elements (Octavia-specific: includes ipvsadmin and keepalived-octavia)

The right elements seem to be included into the virt-dib invocation:

https://github.com/openstack-charmers/octavia-diskimage-retrofit/blob/2dad8d8d2b6615f406ad7339d92c4c1a3a6557d0/src/retrofit/retrofit.sh#L106-L108
virt-dib ${DEBUG} \
# ...
    ubuntu-cloud-archive ubuntu-ppa \
    haproxy-octavia rebind-sshd no-resolvconf amphora-agent \
    sos keepalived-octavia ipvsadmin pip-cache certs-ramfs \
    ubuntu-amphora-agent tuning bug189583

Will look further.

The diskimage-create.sh script from the Octavia repo builds a list of elements to include into an image by concatenating elements to the AMP_element_sequence variable:

https://opendev.org/openstack/octavia/src/commit/bd01ad94dcea3eca7636f1286ceed0753b563a28/diskimage-create/diskimage-create.sh#L459-L461
# Add keepalived-octavia element
AMP_element_sequence="$AMP_element_sequence keepalived-octavia"
AMP_element_sequence="$AMP_element_sequence ipvsadmin"

but then uses diskimage-builder as opposed to virt-dib used by octavia-diskimage-retrofit.

https://libguestfs.org/virt-dib.1.html
"Virt-dib is intended as safe replacement for diskimage-builder and its ramdisk-image-create mode"

This should not matter that much if the right elements get to the built image.

# deployed bionic-train with octavia `tox -e func-target bionic-train-ha`

juju ssh octavia-diskimage-retrofit/0
# the right elements are present on the octavia-diskimage-retrofit unit
$ sudo ls -1 /snap/octavia-diskimage-retrofit/current/usr/local/lib/elements/
amphora-agent
bug1895835
certs-ramfs
debian-networking
growrootfs
haproxy-octavia
ipvsadmin
keepalived-octavia
no-resolvconf
rebind-sshd
remove-sshd
root-passwd
sos
tuning
ubuntu-amphora-agent
ubuntu-archive
ubuntu-cloud-archive
ubuntu-ppa

# saved the image generated by the functional test
openstack image save --file /tmp/amphora-haproxy-x86_64-ubuntu-18.04-20210325 amphora-haproxy-x86_64-ubuntu-18.04-20210325
sudo guestmount -a /tmp/amphora-haproxy-x86_64-ubuntu-18.04-20210325 -i --ro /mnt/amphora

# ipvsadm and keepalived are present on the filesystem of the retrofitted image

find /mnt/amphora -name '*ipvsadm*'
/mnt/amphora/etc/rc2.d/S01ipvsadm
/mnt/amphora/etc/rc5.d/S01ipvsadm
/mnt/amphora/etc/rc0.d/K01ipvsadm
/mnt/amphora/etc/rc4.d/S01ipvsadm
/mnt/amphora/etc/rc3.d/S01ipvsadm
/mnt/amphora/etc/rc1.d/K01ipvsadm
/mnt/amphora/etc/default/ipvsadm
/mnt/amphora/etc/rc6.d/K01ipvsadm
/mnt/amphora/etc/ipvsadm.rules
/mnt/amphora/etc/init.d/ipvsadm
/mnt/amphora/var/lib/dpkg/info/ipvsadm.md5sums
/mnt/amphora/var/lib/dpkg/info/ipvsadm.postrm
/mnt/amphora/var/lib/dpkg/info/ipvsadm.list
/mnt/amphora/var/lib/dpkg/info/ipvsadm.conffiles
/mnt/amphora/var/lib/dpkg/info/ipvsadm.prerm
/mnt/amphora/var/lib/dpkg/info/ipvsadm.postinst
/mnt/amphora/sbin/ipvsadm-restore
/mnt/amphora/sbin/ipvsadm-save
/mnt/amphora/sbin/ipvsadm

find /mnt/amphora -name '*keepalived*'
/mnt/amphora/etc/rc2.d/S01keepalived
/mnt/amphora/etc/rc5.d/S01keepalived
/mnt/amphora/etc/rc0.d/K01keepalived
/mnt/amphora/etc/rc4.d/S01keepalived
/mnt/amphora/etc/rc3.d/S01keepalived
/mnt/amphora/etc/rc1.d/K01keepalived
/mnt/amphora/etc/systemd/system/multi-user.target.wants/keepalived.service
/mnt/amphora/etc/dbus-1/system.d/org.keepalived.Vrrp1.conf
/mnt/amphora/etc/default/keepalived
/mnt/amphora/etc/rc6.d/K01keepalived
/mnt/amphora/etc/keepalived
/mnt/amphora/etc/init.d/keepalived
/mnt/amphora/var/lib/dpkg/info/keepalived.postrm
/mnt/amphora/var/lib/dpkg/info/keepalived.conffiles
/mnt/amphora/var/lib/dpkg/info/keepalived.md5sums
/mnt/amphora/var/lib/dpkg/info/keepalived.list
/mnt/amphora/var/lib/dpkg/info/keepalived.prerm
/mnt/amphora/var/lib/dpkg/info/keepalived.postinst
/mnt/amphora/var/lib/systemd/deb-systemd-helper-enabled/keepalived.service.dsh-also
/mnt/amphora/var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/keepalived.service

So I tried to replicate the scenario in the bug description, however, I was not able to reproduce the issue and the UDP traffic got to a backend successfully (see below). The created amphora has the right set of packages and configuration generated by the amphora-agent.

The scenario I tested with bionic-train (ML2/OVS):

external machine -> provider network -> qrouter ns (non-distributed, non-L3HA router) -> DNAT from LB FIP to LB VIP -> amphora with keepalived+LVS -> backend member IP -> bind9

It would be good to have more information on the networking setup used when the issue was encountered. Specifically, on whether LBs were attached directly to a provider network or via a router and using a FIP (if so, whether that router was distributed, which would be a problem, or L3HA/legacy). Likewise, it would be good to know whether OVN or ML2/OVS was used.

https://paste.ubuntu.com/p/BmcVxjMcxs/ (same as below for readability)

# deployed via `tox -e func-target bionic-train-ha`

ubuntu@dmitriis-bastion:~$ openstack loadbalancer create --name testlb --vip-network-id private_lb_fip_network
+---------------------+--------------------------------------+
| Field | Value |
+---------------------+--------------------------------------+
| admin_state_up | True |
| availability_zone | |
| created_at | 2021-04-06T21:51:05 |
| description | |
| flavor_id | None |
| id | 4273ab40-b760-43b5-9a40-19f7490e3bbd |
| listeners | |
| name | testlb |
| operating_status | OFFLINE |
| pools | |
| project_id | bd5208e7ae354f339567d71e49cf544b |
| provider | amphora |
| provisioning_status | PENDING_CREATE |
| updated_at | None |
| vip_address | 10.42.0.216 |
| vip_network_id | 06ab6573-55df-43ad-ace3-0a4afc1964b9 |
| vip_port_id | 7453d6da-f0f0-4f1a-bc5f-6258e40a2182 |
| vip_qos_policy_id | None |
| vip_subnet_id | 4d011e74-cbda-42ab-b58c-7a5aef4cb5fd |
+---------------------+--------------------------------------+

ubuntu@dmitriis-bastion:~$ openstack loadbalancer listener create --name test-listener --protocol UDP --protocol-port 53 testlb
+-----------------------------+--------------------------------------+
| Field | Value |
+-----------------------------+--------------------------------------+
| admin_state_up | True |
| connection_limit | -1 |
| created_at | 2021-04-06T21:51:58 |
| default_pool_id | None |
| default_tls_conta...