fix(rcm): update the forking behavior in remote config

[avara1986]

Context

The Remote Configuration Publisher/Subscriber System #5464 restarts all pubsub instances when the application forks (for example, gunicorn workers, uwsgi workers, etc.).

Dynamic Instrumentation needs to update the pubsub instance at this point because the probe mechanism should run in the child process. For that, DI needs the callback as the method of an instance of Debugger, which lives in the child process.

https://github.com/DataDog/dd-trace-py/blob/2.x/ddtrace/debugging/_debugger.py#L276

Problem description

When the application forks and restarts the subscribers, this happens before the debugger updates its callback instance.

10348 starting subscribers
10348 restarting the debugger
10348 register callback 4429382528 <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> 4406068560 shared_data 4398747792

This results in the registration of the callback in the child processes but the execution of callbacks using the instance of the parent process.

• Parent process: register a callback on_configuration for DI

94621 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4363974784 Debugger._on_configuration id: 4360362576

• Child processes: register callbacks on_configuration for DI

94638 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id: 4364006016
94639 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id: 4364006016
94640 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id: 4364006016

• Child processes: exec callbacks.

94621 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576
94638 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576
94639 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576
94640 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576

As a result, we're registering callback id 4364006016 but calling 4360362576 (which is the instance of the parent process).

PR Description

This PR removes the restart of publisher-subscriber instances in Remote Configuration at fork and delegates it to the products that have integration with Remote Config, namely AppSec and Dynamic Instrumentation.

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment.
• Backport labels are set in a manner that is consistent with the release branch maintenance policy
• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-11-14 19:24:50

Comparing candidate commit 17f6564 in PR branch avara1986/APPSEC-12170-refactor-remote_config_fork with baseline commit 806d993 in branch 2.x.

Found 0 performance improvements and 3 performance regressions! Performance is the same for 87 metrics, 0 unstable metrics.

scenario:flasksimple-appsec-get

• 🟥 max_rss_usage [+0.987MB; +1.162MB] or [+2.821%; +3.322%]

scenario:flasksimple-appsec-post

• 🟥 max_rss_usage [+1.017MB; +1.224MB] or [+2.919%; +3.513%]

scenario:span-add-metrics

• 🟥 max_rss_usage [+17.076MB; +17.239MB] or [+40.318%; +40.703%]

[P403n1x87]

I think this PR needs to be of type fix since we are fixing an issue, and we also need to backport it on other release branches.

[P403n1x87]

We also need this patch

diff --git a/ddtrace/internal/remoteconfig/worker.py b/ddtrace/internal/remoteconfig/worker.py
index e507dd5be..ec2ae453f 100644
--- a/ddtrace/internal/remoteconfig/worker.py
+++ b/ddtrace/internal/remoteconfig/worker.py
@@ -150,14 +150,12 @@ class RemoteConfigPoller(periodic.PeriodicService):
         try:
             # By enabling on registration we ensure we start the RCM client only
             # if there is at least one registered product.
-            enabled = True
             if not skip_enabled:
-                enabled = self.enable()
+                self.enable()
 
-            if enabled:
-                self._client.register_product(product, pubsub_instance)
-                if not self._client.is_subscriber_running(pubsub_instance):
-                    pubsub_instance.start_subscriber()
+            self._client.register_product(product, pubsub_instance)
+            if not self._client.is_subscriber_running(pubsub_instance):
+                pubsub_instance.start_subscriber()
         except Exception:
             log.debug("error starting the RCM client", exc_info=True)

to fix DI

[github-actions]

The backport to 1.20 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-1.20 1.20
# Navigate to the new working tree
cd .worktrees/backport-1.20
# Create a new branch
git switch --create backport-7548-to-1.20
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1da4fc4761494c16cea7bb547929a1266b699d9b
# Push it to GitHub
git push --set-upstream origin backport-7548-to-1.20
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.20

Then, create a pull request where the base branch is 1.20 and the compare/head branch is backport-7548-to-1.20.

[github-actions]

The backport to 2.0 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.0 2.0
# Navigate to the new working tree
cd .worktrees/backport-2.0
# Create a new branch
git switch --create backport-7548-to-2.0
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1da4fc4761494c16cea7bb547929a1266b699d9b
# Push it to GitHub
git push --set-upstream origin backport-7548-to-2.0
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.0

Then, create a pull request where the base branch is 2.0 and the compare/head branch is backport-7548-to-2.0.

[github-actions]

The backport to 2.1 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.1 2.1
# Navigate to the new working tree
cd .worktrees/backport-2.1
# Create a new branch
git switch --create backport-7548-to-2.1
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1da4fc4761494c16cea7bb547929a1266b699d9b
# Push it to GitHub
git push --set-upstream origin backport-7548-to-2.1
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.1

Then, create a pull request where the base branch is 2.1 and the compare/head branch is backport-7548-to-2.1.