Add debug logs wherever we change current logcontext (`LoggingContext`).
I've had to make this same set of changes over and over as I've been
debugging things so it seems useful enough to include by default.
Instead of tracing things at the `set_current_context(...)` level, I've
added the debug logging on all of the utilities that utilize
`set_current_context(...)`. It's much easier to reason about the log
context changing because of `PreserveLoggingContext` changing things
than an opaque `set_current_context(...)` call.
Revert https://github.com/element-hq/synapse/pull/18849
Go back to our custom `LogContextScopeManager` after trying
OpenTracing's `ContextVarsScopeManager`.
Fix https://github.com/element-hq/synapse/issues/19004
### Why revert?
For reference, with the normal reactor, `ContextVarsScopeManager` worked
just as good as our custom `LogContextScopeManager` as far as I can tell
(and even better in some cases). But since Twisted appears to not fully
support `ContextVar`'s, it doesn't work as expected in all cases.
Compounding things, `ContextVarsScopeManager` was causing errors with
the experimental `SYNAPSE_ASYNC_IO_REACTOR` option.
Since we're not getting the full benefit that we originally desired, we
might as well revert and figure out alternatives for extending the
logcontext lifetimes to support the use case we were trying to unlock
(c.f. https://github.com/element-hq/synapse/pull/18804).
See
https://github.com/element-hq/synapse/issues/19004#issuecomment-3358052171
for more info.
### Does this require backporting and patch releases?
No. Since `ContextVarsScopeManager` operates just as good with the
normal reactor and was only causing actual errors with the experimental
`SYNAPSE_ASYNC_IO_REACTOR` option, I don't think this requires us to
backport and make patch releases at all.
### Maintain cross-links between main trace and background process work
In order to maintain the functionality introduced in https://github.com/element-hq/synapse/pull/18932 (cross-links between the background process trace and currently active trace), we also needed a small change.
Previously, when we were using `ContextVarsScopeManager`, it tracked the tracing scope across the logcontext changes without issue. Now that we're using our own custom `LogContextScopeManager` again, we need to capture the active span from the logcontext before we reset to the sentinel context because of the `PreserveLoggingContext()` below.
Added some tests to ensure we maintain the `run_as_background` tracing behavior regardless of the tracing scope manager we use.
Prefer the utils over raw logcontext manipulation.
Spawning from adding some logcontext debug logs in
https://github.com/element-hq/synapse/pull/18966 and since we're not
logging at the `set_current_context(...)` level (see reasoning there),
this removes some usage of `set_current_context(...)`.
Spawning from adding some logcontext debug logs in
https://github.com/element-hq/synapse/pull/18966 and since we're not
logging at the `set_current_context(...)` level (see reasoning there),
this removes some usage of `set_current_context(...)`.
Specifically, `MockClock.call_later(...)` doesn't handle logcontexts
correctly. It uses the calling logcontext as the callback context
(wrong, as the logcontext could finish before the callback finishes) and
it didn't reset back to the sentinel context before handing back to the
reactor. It was like this since it was [introduced 10+ years
ago](38da9884e7).
Instead of fixing the implementation which would just be a copy of our
normal `Clock`, we can just remove `MockClock`
### Background
As part of Element's plan to support a light form of vhosting (virtual
host) (multiple instances of Synapse in the same Python process), we're
currently diving into the details and implications of running multiple
instances of Synapse in the same Python process.
"Per-tenant logging" tracked internally by
https://github.com/element-hq/synapse-small-hosts/issues/48
### Prior art
Previously, we exposed `server_name` by providing a static logging
`MetadataFilter` that injected the values:
205d9e4fc4/synapse/config/logger.py (L216)
While this can work fine for the normal case of one Synapse instance per
Python process, this configures things globally and isn't compatible
when we try to start multiple Synapse instances because each subsequent
tenant will overwrite the previous tenant.
### What does this PR do?
We remove the `MetadataFilter` and replace it by tracking the
`server_name` in the `LoggingContext` and expose it with our existing
[`LoggingContextFilter`](205d9e4fc4/synapse/logging/context.py (L584-L622))
that we already use to expose information about the `request`.
This means that the `server_name` value follows wherever we log as
expected even when we have multiple Synapse instances running in the
same process.
### A note on logcontext
Anywhere, Synapse mistakenly uses the `sentinel` logcontext to log
something, we won't know which server sent the log. We've been fixing up
`sentinel` logcontext usage as tracked by
https://github.com/element-hq/synapse/issues/18905
Any further `sentinel` logcontext usage we find in the future can be
fixed piecemeal as normal.
d2a966f922/docs/log_contexts.md (L71-L81)
### Testing strategy
1. Adjust your logging config to include `%(server_name)s` in the format
```yaml
formatters:
precise:
format: '%(asctime)s - %(server_name)s - %(name)s - %(lineno)d -
%(levelname)s - %(request)s - %(message)s'
```
1. Start Synapse: `poetry run synapse_homeserver --config-path
homeserver.yaml`
1. Make some requests (`curl
http://localhost:8008/_matrix/client/versions`, etc)
1. Open the homeserver logs and notice the `server_name` in the logs as
expected. `unknown_server_from_sentinel_context` is expected for the
`sentinel` logcontext (things outside of Synapse).
Related to https://github.com/element-hq/synapse/issues/18905
These fixes were split off from
https://github.com/element-hq/synapse/pull/18828 where @devonh was
seeing some test failures because `timeout_deferred(...)` is being
updated to use `Clock` utilities instead of raw `reactor` methods. This
test was failing in that branch/PR until we made this new version that
handles the logcontexts properly.
While the previous version of this test does pass on `develop`, it was
using what appears completely wrong assertions, assumptions, and bad
patterns to make it happen (see diff comments below)
---
Test originally introduced in https://github.com/matrix-org/synapse/pull/4407
Before https://github.com/element-hq/synapse/pull/18849, we we're using
our own custom `LogContextScopeManager` which tied the tracing scope to
the `LoggingContext`. Since we created a new
`BackgroundProcessLoggingContext` any time we
`run_as_background_process(...)`, the trace for the background work was
separate from the trace that kicked of the work as expected (e.g.
request trace is separate from the background process we kicked to fetch
more messages from the federation).
Since we've now switched to the `ContextVarsScopeManager` (in
https://github.com/element-hq/synapse/pull/18849), the tracing scope now
crosses the `LoggingContext` boundaries (and thread boundaries) without
a problem. This means we end up with request traces that include all of
the background work that we've kicked off bloating the trace and making
it hard to understand what's going on.
This PR separates the traces again to how things were before.
Additionally, things are even better now since I added some cross-link
references between the traces to easily be able to jump between.
Follow-up to https://github.com/element-hq/synapse/pull/18849
---
In the before, you can see that the trace is blown up by the background
process (`bgproc.qwer`).
In the after, we now only have a little cross-link marker span
(`start_bgproc.qwer`) to jump to background process trace.
Before | After
--- | ---
<some image> | <some image>
### Testing strategy
1. Run a Jaeger instance
(https://www.jaegertracing.io/docs/1.6/getting-started/)
```shell
$ docker run -d --name jaeger \
-e COLLECTOR_ZIPKIN_HTTP_PORT=9411 \
-p 5775:5775/udp \
-p 6831:6831/udp \
-p 6832:6832/udp \
-p 5778:5778 \
-p 16686:16686 \
-p 14268:14268 \
-p 9411:9411 \
jaegertracing/all-in-one:1.59.0
```
1. Configure Synapse to use tracing:
`homeserver.yaml`
```yaml
## Tracing ##
opentracing:
enabled: true
jaeger_config:
sampler:
type: const
param: 1
logging:
false
```
1. Make sure the optional `opentracing` dependency is installed: `poetry
install --extras all`
1. In the `VersionsRestServlet`, modify it to kick off a dummy
background process (easy to test this way)
```python
from synapse.metrics.background_process_metrics import
run_as_background_process
async def _qwer() -> None:
await self.clock.sleep(1)
run_as_background_process("qwer", "test_server", _qwer)
```
1. Run Synapse: `poetry run synapse_homeserver --config-path
homeserver.yaml`
1. Fire off a version requests: `curl
http://localhost:8008/_matrix/client/versions`
1. Visit http://localhost:16686/search to view the traces
- Select the correct service
- Look for the `VersionsRestServlet` operation
- Press 'Find Traces' button
- Select the relevant trace
- Notice how the trace isn't bloated
- Look for the `start_bgproc.qwer` span cross-linking to the background
process
- Jump to the other trace using the cross-link reference ->
`bgproc.qwer`
