Document prerequisite of enabling antrea service proxy

[tnqn]

Describe the bug
I was trying the feature AntreaProxy but met pod connection issue after enabling it.
Thera are logs saying something is wrong:

E0701 09:47:22.690551       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 136 0 0 0 62 79 78 70 0 0 0 8 253 0 0 0 4 0 0 0 1 4 14 0 112 0 0 0 62 0 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 30 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 10 128 0 10 2 8 0 0 0 0 0 0 0 0 4 0 48 0 0 0 0 255 255 0 40 0 0 35 32 0 35 0 0 0 0 0 0 255 240 31 0 0 0 0 0 255 255 0 16 0 0 35 32 0 36 0 0 0 0 0 0]
E0701 09:47:22.734358       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 145 79 78 70 0 0 0 8 253 0 0 0 11 0 0 0 1 4 14 0 176 0 0 0 145 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 6 0 1 6 4 192 168 10 12 0 1 9 8 0 2 25 43 0 7 255 255 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 192 168 10 12 192 168 10 12 25 43 25 43 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]
E0701 09:47:22.736663       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 156 79 78 70 0 0 0 8 253 0 0 0 13 0 0 0 1 4 14 0 176 0 0 0 156 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 6 0 1 6 4 172 30 0 17 0 1 9 8 0 2 35 193 0 7 255 255 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 172 30 0 17 172 30 0 17 35 193 35 193 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]
E0701 09:47:22.737544       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 163 79 78 70 0 0 0 8 253 0 0 0 14 0 0 0 1 4 14 0 176 0 0 0 163 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 6 0 1 6 4 172 30 0 18 0 1 9 8 0 2 35 193 0 7 255 255 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 172 30 0 18 172 30 0 18 35 193 35 193 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]
E0701 09:47:22.739775       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 176 79 78 70 0 0 0 8 253 0 0 0 16 0 0 0 1 4 14 0 176 0 0 0 176 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 17 0 1 6 4 172 30 0 18 0 1 9 8 0 2 0 53 0 7 255 255 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 172 30 0 18 172 30 0 18 0 53 0 53 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]
E0701 09:47:22.740579       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 183 79 78 70 0 0 0 8 253 0 0 0 17 0 0 0 1 4 14 0 176 0 0 0 183 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 17 0 1 9 8 0 2 0 53 0 7 255 255 0 1 6 4 172 30 0 17 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 172 30 0 17 172 30 0 17 0 53 0 53 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]
E0701 09:47:22.743385       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 196 79 78 70 0 0 0 8 253 0 0 0 19 0 0 0 1 4 14 0 176 0 0 0 196 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 6 0 1 9 8 0 2 0 53 0 7 255 255 0 1 6 4 172 30 0 17 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 172 30 0 17 172 30 0 17 0 53 0 53 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]
E0701 09:47:22.744274       1 ofSwitch.go:330] Received Vendor error msg: [4 4 0 200 0 0 0 203 79 78 70 0 0 0 8 253 0 0 0 20 0 0 0 1 4 14 0 176 0 0 0 203 0 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 42 0 0 0 0 0 0 200 255 255 255 255 255 255 255 255 255 255 255 255 0 0 0 0 0 1 0 35 128 0 10 2 8 0 128 0 20 1 6 0 1 6 4 172 30 0 18 0 1 9 8 0 2 0 53 0 7 255 255 0 0 0 0 0 0 4 0 88 0 0 0 0 255 255 0 80 0 0 35 32 0 35 0 1 0 0 0 0 255 240 50 0 0 0 0 0 255 255 0 32 0 0 35 32 0 36 0 0 0 2 0 51 172 30 0 18 172 30 0 18 0 53 0 53 0 0 0 0 255 255 0 24 0 0 35 32 0 7 0 31 0 1 214 4 0 0 0 0 0 0 0 33]

It's impossible understand what the error messages mean.

I can find ovs-vswitchd logs with plain message:

2020-07-01T09:50:21.698Z|00061|ofproto_dpif|WARN|Rejecting ct action because datapath does not support nat (your kernel module may be out of date)
2020-07-01T09:50:21.698Z|00062|connmgr|INFO|br-int<->unix#0: sending NXBAC_CT_DATAPATH_SUPPORT error reply to ONFT_BUNDLE_ADD_MESSAGE message
2020-07-01T09:50:21.701Z|00063|ofproto_dpif|WARN|Rejecting ct action because datapath does not support nat (your kernel module may be out of date)
2020-07-01T09:50:21.701Z|00064|connmgr|INFO|br-int<->unix#0: sending NXBAC_CT_DATAPATH_SUPPORT error reply to ONFT_BUNDLE_ADD_MESSAGE message
2020-07-01T09:50:21.703Z|00065|connmgr|INFO|br-int<->unix#0: sending NXBAC_CT_DATAPATH_SUPPORT error reply to ONFT_BUNDLE_ADD_MESSAGE message
2020-07-01T09:50:21.706Z|00066|connmgr|INFO|br-int<->unix#0: sending NXBAC_CT_DATAPATH_SUPPORT error reply to ONFT_BUNDLE_ADD_MESSAGE message

Apparently my kernel module is too old, but it meets the requirement documented in https://github.com/vmware-tanzu/antrea/blob/master/docs/getting-started.md#ensuring-requirements-are-satisfied.

As for OVS, when using the built-in kernel module, kernel version >= 4.4 is required. On the other hand, when building it from OVS sources, OVS version >= 2.6.0 is required.

Mine is 4.4.0-45-generic.

The prerequisite of AntreaProxy feature should be documented, perhaps as a note in a doc explaining all experimental features.

To Reproduce
Enabling AntreaProxy with kernel module 4.4.0.

Expected

• The prerequisite of AntreaProxy feature should be documented
• The error message of openflow should be readable

Versions:
Please provide the following information:

• Antrea version (Docker image tag). v0.8.0-dev-c7d34f8
• Kubernetes version (use kubectl version). If your Kubernetes components have different versions, please provide the version for all of them.
• Container runtime: which runtime are you using (e.g. containerd, cri-o, docker) and which version are you using?
• Linux kernel version on the Kubernetes Nodes (uname -r). 4.4.0-45-generic
• If you chose to compile the Open vSwitch kernel module manually instead of using the kernel module built into the Linux kernel, which version of the OVS kernel module are you using? Include the output of modinfo openvswitch for the Kubernetes Nodes.

filename:       /lib/modules/4.4.0-45-generic/kernel/net/openvswitch/openvswitch.ko
license:        GPL
description:    Open vSwitch switching datapath
srcversion:     21F49064BF4E207E1504046
depends:        nf_conntrack,libcrc32c,nf_defrag_ipv6
intree:         Y
vermagic:       4.4.0-45-generic SMP mod_unload modversions

[antoninbas]

@tnqn just a quick note that the parsing of the OF error message is already tracked by #571, but according to @wenyingd this is a pretty large amount of work.

Agreed for a separate document with list of experimental features and their requirements. I can take a stab at that.