Sequence BWC logic consists of two elements:
1) Wire level BWC using stream versions.
2) A changed to the global checkpoint maintenance semantics.
For the sequence number infra to work with a mixed version clusters, we have to consider situation where the primary is on an old node and replicas are on new ones (i.e., the replicas will receive operations without seq#) and also the reverse (i.e., the primary sends operations to a replica but the replica can't process the seq# and respond with local checkpoint). An new primary with an old replica is a rare because we do not allow a replica to recover from a new primary. However, it can occur if the old primary failed and a new replica was promoted or during primary relocation where the source primary is treated as a replica until the master starts the target.
1) Old Primary & New Replica - this case is easy as is taken care of by the wire level BWC. All incoming requests will have their seq# set to `UNASSIGNED_SEQ_NO`, which doesn't confuse the local checkpoint logic (keeping it at `NO_OPS_PERFORMED`)
2) New Primary & Old replica - this one is trickier as the global checkpoint service currently takes all in sync replicas into consideration for the global checkpoint calculation. In order to deal with old replicas, we change the semantics to say all *new node* in sync replicas. That means the replicas on old nodes don't count for the global checkpointing. In this state the seq# infra is not fully operational (you can't search on it, because copies may miss it) but it is maintained on shards that can support it. The old replicas will have to go through a file based recovery at some point and will get the seq# information at that point. There is still an edge case where a new primary fails and an old replica takes over. I'lll discuss this one with @ywelsch as I prefer to avoid it completely.
This PR also re-enables the BWC tests which were disabled. As such it had to fix any BWC issue that had crept in. Most notably an issue with the removal of the `timestamp` field in #21670.
The commit also includes a fix for the default value of the seq number field in replicated write requests (it was 0 but should be -2), that surface some other minor bugs which are fixed as well.
Last - I added some debugging tools like more sane node names and forcing replication request to implement a `toString`
There is not yet a BWC layer in sequence numbers. This commit sets the
BWC version to 6.0.0 for the BWC and rolling upgrade tests until this
BWC layer is built.
This commit enables real BWC testing against a 5.1 snapshot. All
REST tests plus rolling upgrade test now run against a mixed version
cross major version cluster.
Change version, required a minor fix in the RPM building.
In case of a alpha/beta version, the release will contain alpha/beta
as the RPM version cannot contains dashes/tildes.
This change adds the infrastructure to run the rest tests on a multi-node
cluster that users 2 different minor versions of elasticsearch. It doesn't implement
any dedicated BWC tests but rather leverages the existing REST tests.
Since we don't have a real version to test against, the tests uses the current version
until the first minor / RC is released to ensure the infrastructure works.
Relates to #14406Closes#17072
Ali Beyad
Nik Everett
Boaz Leskes
javanna
Jason Tedor
Simon Willnauer
Clinton Gormley
Adrien Grand
Ryan Ernst
Alexander Reelsen