This is an early detector for a multitude of other symptoms, some of
which cause panics.
When creating the ring we record the paxos-supplied normalised list of
peers used for seeding. This subsequently gets gossipped around as
part of the Ring data structure, and checked in ring.Merge that it is
the same for the recipient.
There are some subtleties due to the desire to maintain backward
compatibility and deal with empty rings
- The gossip gob decoder will ignore the Ring.Seeds field when an old
weave receives a Ring from a new weave. So everything on the old
weave will just continue to work as before.
- The gossip gob decoder will set the Ring.Seeds field to nil when a
new weave receives a Ring from an old weave. We therefore omit the
seed equivalence check when the received Seeds slice is empty.
- Our ring may not have any seeds - either because it is empty or was
created from a ring received from an old weave. We therefore a) omit
the seed equivalence check in that situation, and b) set our seeds
to those received. Note that this allows us to learn about the seeds
well after ring creation - a situation which may arise when
receiving gossip from a mixture of old and new weaves.
Fixes#1463.
Matthias Radestock
7e0ae6112c