Fixes https://emqx.atlassian.net/browse/EMQX-10405
The problem here was that, for async requests, ehttpc responses of the form `{ok, 4__, _,
_}` and similar were being treated as successes.
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.
This is a performance improvement for webhook bridge.
Since this bridge is called using `async` callback mode, and `ehttpc`
frequently returns errors of the form `normal` and `{shutdown,
normal}` that are retried "for free" by `ehttpc`, we add this behavior
to async requests as well. Other errors are retried too, but they are
not "free": 3 attempts are made at a maximum.
This is important because, when using buffer workers, we should avoid
making them enter the `blocked` state, since that halts all progress
and makes throughput plummet.
When using async mode with the webhook bridge, queued messages that are
not fully processed when the connection times out could be lost. This
commit fixes this by letting the bridge return a recoverable_error when
this happen. The message send will then be retried in sync mode by the
emqx_resource_buffer_worker.
Fixes: https://emqx.atlassian.net/browse/EMQX-8974
Thales Macedo Garitezi