See [code changes](https://github.com/coreos/etcd/compare/v3.1.14...v3.1.15) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
### etcd server
- Purge old [`*.snap.db` snapshot files](https://github.com/coreos/etcd/pull/7967).
- Previously, etcd did not respect `--max-snapshots` flag to purge old `*.snap.db` files.
- Now, etcd purges old `*.snap.db` files to keep maximum `--max-snapshots` number of files on disk.
### Go
- Compile with [*Go 1.8.7*](https://golang.org/doc/devel/release.html#go1.8).
See [code changes](https://github.com/coreos/etcd/compare/v3.1.13...v3.1.14) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
- Add [`--initial-election-tick-advance`](https://github.com/coreos/etcd/pull/9591) flag to configure initial election tick fast-forward.
- By default, `--initial-election-tick-advance=true`, then local member fast-forwards election ticks to speed up "initial" leader election trigger.
- This benefits the case of larger election ticks. For instance, cross datacenter deployment may require longer election timeout of 10-second. If true, local node does not need wait up to 10-second. Instead, forwards its election ticks to 8-second, and have only 2-second left before leader election.
- Major assumptions are that: cluster has no active leader thus advancing ticks enables faster leader election. Or cluster already has an established leader, and rejoining follower is likely to receive heartbeats from the leader after tick advance and before election timeout.
- However, when network from leader to rejoining follower is congested, and the follower does not receive leader heartbeat within left election ticks, disruptive election has to happen thus affecting cluster availabilities.
- Now, this can be disabled by setting `--initial-election-tick-advance=false`.
- Disabling this would slow down initial bootstrap process for cross datacenter deployments. Make tradeoffs by configuring `--initial-election-tick-advance` at the cost of slow initial bootstrap.
See [code changes](https://github.com/coreos/etcd/compare/v3.1.12...v3.1.13) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
- Adjust [election timeout on server restart](https://github.com/coreos/etcd/pull/9415) to reduce [disruptive rejoining servers](https://github.com/coreos/etcd/issues/9333).
- Previously, etcd fast-forwards election ticks on server start, with only one tick left for leader election. This is to speed up start phase, without having to wait until all election ticks elapse. Advancing election ticks is useful for cross datacenter deployments with larger election timeouts. However, it was affecting cluster availability if the last tick elapses before leader contacts the restarted node.
- Now, when etcd restarts, it adjusts election ticks with more than one tick left, thus more time for leader to prevent disruptive restart.
See [code changes](https://github.com/coreos/etcd/compare/v3.1.11...v3.1.12) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.10...v3.1.11) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.9...v3.1.10) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.8...v3.1.9) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.7...v3.1.8) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.6...v3.1.7) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.5...v3.1.6) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.4...v3.1.5) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.3...v3.1.4) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.2...v3.1.3) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.1...v3.1.2) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.1.0...v3.1.1) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
See [code changes](https://github.com/coreos/etcd/compare/v3.0.0...v3.1.0) and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md) for any breaking changes. **Again, before running upgrades from any previous release, please make sure to read change logs below and [v3.1 upgrade guide](https://github.com/coreos/etcd/blob/master/Documentation/upgrades/upgrade_3_1.md).**
- Deprecated following gRPC metrics in favor of [go-grpc-prometheus](https://github.com/grpc-ecosystem/go-grpc-prometheus).
-`etcd_grpc_requests_total`
-`etcd_grpc_requests_failed_total`
-`etcd_grpc_active_streams`
-`etcd_grpc_unary_requests_duration_seconds`
### Dependency
- Upgrade [`github.com/ugorji/go/codec`](https://github.com/ugorji/go) to [**`ugorji/go@9c7f9b7`**](https://github.com/ugorji/go/commit/9c7f9b7a2bc3a520f7c7b30b34b7f85f47fe27b6), and [regenerate v2 `client`](https://github.com/coreos/etcd/pull/6945).
### Security, Authentication
See [security doc](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/security.md) for more details.
- SRV records (e.g., infra1.example.com) must match the discovery domain (i.e., example.com) if no custom certificate authority is given.
-`TLSConfig.ServerName` is ignored with user-provided certificates for backwards compatibility; to be deprecated.
- For example, `etcd --discovery-srv=example.com` will only authenticate peers/clients when the provided certs have root domain `example.com` as an entry in Subject Alternative Name (SAN) field.
- v3.0 and v3.1 with `--auto-compaction-retention=10` run periodic compaction on v3 key-value store for every 10-hour.
- Compactor only supports periodic compaction.
- Compactor records latest revisions every 5-minute, until it reaches the first compaction period (e.g. 10-hour).
- In order to retain key-value history of last compaction period, it uses the last revision that was fetched before compaction period, from the revision records that were collected every 5-minute.
- When `--auto-compaction-retention=10`, compactor uses revision 100 for compact revision where revision 100 is the latest revision fetched from 10 hours ago.
- If compaction succeeds or requested revision has already been compacted, it resets period timer and starts over with new historical revision records (e.g. restart revision collect and compact for the next 10-hour period).
