This patch allows endpoints to complete servicing connections while
being removed from a service. The fix is entirely within libnetwork
and requires no changes to the moby codebase proper. It operates
by initially down-weighting a container endpoint in the load balancer
to 0 while keeping the endpoint present in the load balancer. This
allows traffic to continue to flow to the endpoint while preventing new
connections from going to the endpoint. This allows the container
to complete requests during the "stop_grace_period" and then exit when
finished without interruption of service.
This change requires propagating the status of disabled service
endpoints via the networkDB. Accordingly, the patch includes both code
to generate and handle service update messages. It also augments the
service structure with a ServiceDisabled boolean to convey whether an
endpoint should ultimately be removed or just disabled. This,
naturally, required a rebuild of the protocol buffer code.
The protocol buffer encoding is designed to support additions of fields
to messages in a backwards-compatible manner. Protocol buffer
unmarshalling code automatically skips past any fields that it isn't
aware of. As a result, an older moby daemon without this fix can
receive and will process correctly networkDB messages from newer moby
daemons with this patch.
As it turns out, the additional field is simply a bool that is otherwise
irrelevent on networkDB create and delete events. So its absence in
older moby daemon processing has no impact. However, the fix leverages
the "update" networkDB message which was previously unused in
libnetwork. Although older libnetwork implementations parse the message
cleanly, they will see the message as unexpected and as such issue a log
at error level indicating the receipt of such.
Other than this there should be no other negative impact for use of this
patch in mixed environments. (Although older mobys won't be able to
gracefully downgrade connections on their nodes of course.)
Signed-off-by: Chris Telfer <ctelfer@docker.com>
Upstream-commit: 50dbdeff9fd186bb0e9926996436e1f56529a831
Component: engine
