In the case that follower recieves a snapshot from leader
and crashes before renaming xxx.snap.db to db but after
snapshot has persisted to .wal and .snap, restarting
follower results loading old db, new .wal, and new .snap.
This will causes a index mismatch between snap metadata index
and consistent index from db.
This pr forces an ordering where saving/renaming db must
happen after snapshot is persisted to wal and snap file.
this guarantees wal and snap files are newer than db.
on server restart, etcd server checks if snap index > db consistent index.
if yes, etcd server attempts to load xxx.snap.db where xxx=snap index
if there is any and panic other wise.
FIXES#7628
Problem is:
`Step1`: `etcdserver/raft.go`'s `Ready` process routine sends config-change entries via `r.applyc <- ap` (https://github.com/coreos/etcd/blob/master/etcdserver/raft.go#L193-L203)
`Step2`: `etcdserver/server.go`'s `*EtcdServer.run` routine receives this via `ap := <-s.r.apply()` (https://github.com/coreos/etcd/blob/master/etcdserver/server.go#L735-L738)
`StepA`: `Step1` proceeds without sync, right after sending `r.applyc <- ap`.
`StepB`: `Step2` proceeds without sync, right after `sched.Schedule(s.applyAll(&ep,&ap))`.
`StepC`: `etcdserver` tries to sync with `s.applyAll(&ep,&ap)` by calling `rh.waitForApply()`.
`rh.waitForApply()` waits for all pending jobs to finish in `pkg/schedule`
side. However, the order of `StepA`,`StepB`,`StepC` is not guaranteed. It
is possible that `StepC` happens first, and proceeds without waiting on
apply. And the restarting member comes back as a leader in single-node
cluster, when there is no synchronization between apply-layer and
config-change Raft entry apply. Confirmed with more debugging lines below,
only reproducible with slow CPU VM (~2 vCPU).
```
~:24.005397 I | etcdserver: starting server... [version: 3.2.0+git, cluster version: to_be_decided]
~:24.011136 I | etcdserver: [DEBUG] 29b2d24047a277df waitForApply before
~:24.011194 I | etcdserver: [DEBUG] 29b2d24047a277df starts wait for 0 pending jobs
~:24.011234 I | etcdserver: [DEBUG] 29b2d24047a277df finished wait for 0 pending jobs (current pending 0)
~:24.011268 I | etcdserver: [DEBUG] 29b2d24047a277df waitForApply after
~:24.011348 I | etcdserver: [DEBUG] [0] 29b2d24047a277df is scheduling conf change on 29b2d24047a277df
~:24.011396 I | etcdserver: [DEBUG] [1] 29b2d24047a277df is scheduling conf change on 5edf80e32a334cf0
~:24.011437 I | etcdserver: [DEBUG] [2] 29b2d24047a277df is scheduling conf change on e32e31e76c8d2678
~:24.011477 I | etcdserver: [DEBUG] 29b2d24047a277df scheduled conf change on 29b2d24047a277df
~:24.011509 I | etcdserver: [DEBUG] 29b2d24047a277df scheduled conf change on 5edf80e32a334cf0
~:24.011545 I | etcdserver: [DEBUG] 29b2d24047a277df scheduled conf change on e32e31e76c8d2678
~:24.012500 I | etcdserver: [DEBUG] 29b2d24047a277df applyConfChange on 29b2d24047a277df before
~:24.013014 I | etcdserver/membership: added member 29b2d24047a277df [unix://127.0.0.1:2100515039] to cluster 9250d4ae34216949
~:24.013066 I | etcdserver: [DEBUG] 29b2d24047a277df applyConfChange on 29b2d24047a277df after
~:24.013113 I | etcdserver: [DEBUG] 29b2d24047a277df applyConfChange on 29b2d24047a277df after trigger
~:24.013158 I | etcdserver: [DEBUG] 29b2d24047a277df applyConfChange on 5edf80e32a334cf0 before
~:24.013666 W | etcdserver: failed to send out heartbeat on time (exceeded the 10ms timeout for 11.964739ms)
~:24.013709 W | etcdserver: server is likely overloaded
~:24.013750 W | etcdserver: failed to send out heartbeat on time (exceeded the 10ms timeout for 12.057265ms)
~:24.013775 W | etcdserver: server is likely overloaded
~:24.013950 I | raft: 29b2d24047a277df is starting a new election at term 4
~:24.014012 I | raft: 29b2d24047a277df became candidate at term 5
~:24.014051 I | raft: 29b2d24047a277df received MsgVoteResp from 29b2d24047a277df at term 5
~:24.014107 I | raft: 29b2d24047a277df became leader at term 5
~:24.014146 I | raft: raft.node: 29b2d24047a277df elected leader 29b2d24047a277df at term 5
```
I am printing out the number of pending jobs before we call
`sched.WaitFinish(0)`, and there was no pending jobs, so it returned
immediately (before we schedule `applyAll`).
This is the root cause to:
- https://github.com/coreos/etcd/issues/7595
- https://github.com/coreos/etcd/issues/7739
- https://github.com/coreos/etcd/issues/7802
`sched.WaitFinish(0)` doesn't work when `len(f.pendings)==0` and
`f.finished==0`. Config-change is the first job to apply, so
`f.finished` is 0 in this case.
`f.finished` monotonically increases, so we need `WaitFinish(finished+1)`.
And `finished` must be the one before calling `Schedule`. This is safe
because `Schedule(applyAll)` is the only place adding jobs to `sched`.
Then scheduler waits on the single job of `applyAll`, by getting the
current number of finished jobs before sending `Schedule`.
Or just make it be blocked until `applyAll` routine triggers on the
config-change job. This patch just removes `waitForApply`, and
signal `raftDone` to wait until `applyAll` finishes applying entries.
Confirmed that it fixes the issue, as below:
```
~:43.198354 I | rafthttp: started streaming with peer 36cda5222aba364b (stream MsgApp v2 reader)
~:43.198740 I | etcdserver: [DEBUG] 3988bc20c2b2e40c waitForApply before
~:43.198836 I | etcdserver: [DEBUG] 3988bc20c2b2e40c starts wait for 0 pending jobs, 1 finished jobs
~:43.200696 I | integration: launched 3169361310155633349 ()
~:43.201784 I | etcdserver: [DEBUG] [0] 3988bc20c2b2e40c is scheduling conf change on 36cda5222aba364b
~:43.201884 I | etcdserver: [DEBUG] [1] 3988bc20c2b2e40c is scheduling conf change on 3988bc20c2b2e40c
~:43.201965 I | etcdserver: [DEBUG] [2] 3988bc20c2b2e40c is scheduling conf change on cf5d6cbc2a121727
~:43.202070 I | etcdserver: [DEBUG] 3988bc20c2b2e40c scheduled conf change on 36cda5222aba364b
~:43.202139 I | etcdserver: [DEBUG] 3988bc20c2b2e40c scheduled conf change on 3988bc20c2b2e40c
~:43.202204 I | etcdserver: [DEBUG] 3988bc20c2b2e40c scheduled conf change on cf5d6cbc2a121727
~:43.202444 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on 36cda5222aba364b (request ID: 0) before
~:43.204486 I | etcdserver/membership: added member 36cda5222aba364b [unix://127.0.0.1:2100913646] to cluster 425d73f1b7b01674
~:43.204588 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on 36cda5222aba364b (request ID: 0) after
~:43.204703 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on 36cda5222aba364b (request ID: 0) after trigger
~:43.204791 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on 3988bc20c2b2e40c (request ID: 0) before
~:43.205689 I | etcdserver/membership: added member 3988bc20c2b2e40c [unix://127.0.0.1:2101113646] to cluster 425d73f1b7b01674
~:43.205783 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on 3988bc20c2b2e40c (request ID: 0) after
~:43.205929 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on 3988bc20c2b2e40c (request ID: 0) after trigger
~:43.206056 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on cf5d6cbc2a121727 (request ID: 0) before
~:43.207353 I | etcdserver/membership: added member cf5d6cbc2a121727 [unix://127.0.0.1:2100713646] to cluster 425d73f1b7b01674
~:43.207516 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on cf5d6cbc2a121727 (request ID: 0) after
~:43.207619 I | etcdserver: [DEBUG] 3988bc20c2b2e40c applyConfChange on cf5d6cbc2a121727 (request ID: 0) after trigger
~:43.207710 I | etcdserver: [DEBUG] 3988bc20c2b2e40c finished scheduled conf change on 36cda5222aba364b
~:43.207781 I | etcdserver: [DEBUG] 3988bc20c2b2e40c finished scheduled conf change on 3988bc20c2b2e40c
~:43.207843 I | etcdserver: [DEBUG] 3988bc20c2b2e40c finished scheduled conf change on cf5d6cbc2a121727
~:43.207951 I | etcdserver: [DEBUG] 3988bc20c2b2e40c finished wait for 0 pending jobs (current pending 0, finished 1)
~:43.208029 I | rafthttp: started HTTP pipelining with peer cf5d6cbc2a121727
~:43.210339 I | rafthttp: peer 3988bc20c2b2e40c became active
~:43.210435 I | rafthttp: established a TCP streaming connection with peer 3988bc20c2b2e40c (stream MsgApp v2 reader)
~:43.210861 I | rafthttp: started streaming with peer 3988bc20c2b2e40c (writer)
~:43.211732 I | etcdserver: [DEBUG] 3988bc20c2b2e40c waitForApply after
```
Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>
raftNode was being initialized in start(), which was causing
hangs when trying to stop the etcd server since the stop channel
would not be initialized in time for the stop call. Instead,
setup non-configurable bits in a constructor.
Fixes#7668
When apply-layer sees configuration change entry in
raft.Ready.CommittedEntries, the server should not proceed
until that entry is applied. Otherwise, follower's raft
layer advances, possibly election-timeouts, and becomes
the leader in single-node cluster, before add-node conf
change of other nodes is applied.
Fix https://github.com/coreos/etcd/issues/7595.
Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>
If we promote the lessor before finish applying all
entries from the last term, we might incorrectly renew
the already revoked leases.
Here is an example:
- Term 1: revoke lease A accepted by raft
- Old leader failed, new election happened
- Term 2: promote
- Term 2: keep alive A succeed. A now has 10 seconds TTL
- Term 2: revoke lease A from Term 1 got committed and applied
- Term 2: the lease A with 10 seconds TTL is revoked
To solve this, the new leader MUST apply all entries from old term
before promote its lessor to start accept renew requests.
The new leader needs to refresh with an extened TTL to gracefully handle
the potential concurrent leader issue. Clients might still send keep alive
to old leader until the old leader itself gives up leadership at most after
an election timeout.
The raft loop would block on the applier's done channel after
persisting the raft messages; the latency could cause dropped network
messages. Instead, asynchronously notify the applier with a buffered
channel when the raft writes complete.
This fixes the problem that proposal cannot be applied.
When start the etcdserver.run loop, it expects to get the latest
existing snapshot. It should not attempt to request one because the loop
is the entity to create the snapshot.
snapshotStore is the store of snapshot, and it supports to get latest snapshot
and save incoming snapshot.
raftStorage supports to get latest snapshot when v3demo is open.
Before this PR, the timeout caused by leader election returns:
```
14:45:37 etcd2 | 2015-08-12 14:45:37.786349 E | etcdhttp: got unexpected
response error (etcdserver: request timed out)
```
After this PR:
```
15:52:54 etcd1 | 2015-08-12 15:52:54.389523 E | etcdhttp: etcdserver:
request timed out, possibly due to leader down
```
It uses heartbeat interval and election timeout to estimate the
commit timeout for internal requests.
This PR helps etcd survive under high roundtrip-time environment,
e.g., globally-deployed cluster.
Follow the simple rule in the atomic package:
"On both ARM and x86-32, it is the caller's responsibility to arrange
for 64-bit alignment of 64-bit words accessed atomically. The first word
in a global variable or in an allocated struct or slice can be relied
upon to be 64-bit aligned."
Tested on a system with /proc/cpuinfo reporting:
processor : 0
model name : ARMv7 Processor rev 1 (v7l)
Features : swp half thumb fastmult vfp edsp thumbee neon vfpv3
tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc0d
CPU revision : 1
The behavior accelarates the happen of the first-time leader election,
so the cluster could elect its leader fast. Technically, it could
help to reduce `electionMs - heartbeatMs` wait time for the first leader election.
Main usage:
1. Quick start for the local cluster when setting a little longer
election timeout
2. Quick start for the global cluster, which sets election timeout to
its maximum 50s.
dvonthenen