See:
https://emqx.atlassian.net/wiki/spaces/P/pages/612368639/open+e5.1+remove+auto+restart+interval+from+buffer+worker+resource+options
Current problem:
In 5.0.x, we have two timer options that control the state changing of buffer worker
resources: auto_restart_interval and health_check_interval.
- auto_restart_interval controls how often the resource attempts to transition from
disconnected to connected.
- health_check_interval controls how often the resource is checked and potentially moved
from connected to disconnected or connecting.
The existence of two independent timers for very similar purposes is confusing to users,
QA and even developers. Also, an intimately related configuration is request_timeout,
which can interact badly with auto_restart_interval if the latter is poorly configured:
requests may always expire if request_timeout < auto_restart_interval and if the resource
enters the disconnected state. For health_check_interval, we attempt to derive a sane
default that gives requests a chance to retry (if request timeout is finite, then the
resource retries requests with a period of min(health_check_interval, request_timeout /
3).
Another problem with the separate auto_restart_interval is that its default value (60 s)
is too high when compared to the default request timeout and health check, leading to the
problems described above if not tuned.
Proposed solution:
We propose to drop auto_restart_interval in favor of health_check_interval, which will be
used for both disconnected -> connected and connected -> {disconnected, connecting}
transition checks. With that, the resource will attempt to reconnect at the same interval
as the health check, which currently is 15 s.
Also, as two smaller changes to accompany this one:
- Increase the default request_timeout from 15 s to 45 s.
- Rename request_timeout to request_ttl.
Fixes https://emqx.atlassian.net/browse/EMQX-9536
Note: since GCP PubSub is not shared by any authn/authz backend,
there's no need to separate its connector into another app.
Fixes https://emqx.atlassian.net/browse/EMQX-9130
Since buffer workers always support async calls ("outer calls"), we
should decouple those two call modes (inner and outer), and avoid
exposing the inner call configuration to user to avoid complexity.
For bridges that currently only allow sync query modes, we should
allow them to be configured with async. That means basically all
bridge types except Kafka Producer.
Zaiming (Stone) Shi