This ensures that server-to-server streaming RPC calls use the tls
wrapped connections.
Prior to this, `streamingRpcImpl` function uses tls for setting header
and invoking the rpc method, but returns unwrapped tls connection.
Thus, streaming writes fail with tls errors.
This tls streaming bug existed since 0.8.0[1], but PR #5654[2]
exacerbated it in 0.9.2. Prior to PR #5654, nomad client used to
shuffle servers at every heartbeat -- `servers.Manager.setServers`[3]
always shuffled servers and was called by heartbeat code[4]. Shuffling
servers meant that a nomad client would heartbeat and establish a
connection against all nomad servers eventually. When handling
streaming RPC calls, nomad servers used these local connection to
communicate directly to the client. The server-to-server forwarding
logic was left mostly unexercised.
PR #5654 means that a nomad client may connect to a single server only
and caused the server-to-server forward streaming RPC code to get
exercised more and unearthed the problem.
[1] https://github.com/hashicorp/nomad/blob/v0.8.0/nomad/rpc.go#L501-L515
[2] https://github.com/hashicorp/nomad/pull/5654
[3] https://github.com/hashicorp/nomad/blob/v0.9.1/client/servers/manager.go#L198-L216
[4] https://github.com/hashicorp/nomad/blob/v0.9.1/client/client.go#L1603
Rename SnapshotAfter to SnapshotMinIndex. The old name was not
technically accurate. SnapshotAtOrAfter is more accurate, but wordy and
still lacks context about what precisely it is at or after (the index).
SnapshotMinIndex was chosen as it describes the action (snapshot), a
constraint (minimum), and the object of the constraint (index).
The previous commit prevented evaluating plans against a state snapshot
which is older than the snapshot at which the plan was created. This is
correct and prevents failures trying to retrieve referenced objects that
may not exist until the plan's snapshot. However, this is insufficient
to guarantee consistency if the following events occur:
1. P1, P2, and P3 are enqueued with snapshot @ 100
2. Leader evaluates and applies Plan P1 with snapshot @ 100
3. Leader evaluates Plan P2 with snapshot+P1 @ 100
4. P1 commits @ 101
4. Leader evaluates applies Plan P3 with snapshot+P2 @ 100
Since only the previous plan is optimistically applied to the state
store, the snapshot used to evaluate a plan may not contain the N-2
plan!
To ensure plans are evaluated and applied serially we must consider all
previous plan's committed indexes when evaluating further plans.
Therefore combined with the last PR, the minimum index at which to
evaluate a plan is:
min(previousPlanResultIndex, plan.SnapshotIndex)
