While influxdb-relay does provide some level of high availability, there are
a few scenarios that need to be accounted for:
- Continuous queries will still only write their results locally. If a server goes down, the continuous query will have to be backfilled after the data has been recovered for that instance.
- Overwriting points is potentially unpredictable. For example, given servers A
and B, if B is down, and point X is written (we'll call the value X1) just
before B comes back online, that write is queued behind every other write
that occurred while B was offline. Once B is back online, the first buffered
write succeeds, and all new writes are now allowed to pass-through. At this
point (before X1 is written to B), X is written again (with value X2 this
time) to both A and B. When the relay reaches the end of B's buffered writes,
it will write X (with value X1) to B... At this point A now has X2, but B has
X1.
- It is probably best to avoid re-writing points (if possible). Otherwise, please be aware that overwriting the same field for a given point can lead to data differences.
- This could potentially be mitigated by waiting for the buffer to flush before opening writes back up to being passed-through.
- When a request is buffered, the client recieves a
202HTTP response indicating that his request will be fullfilled later. So the client will never reveive the response of the actual request.