Alright, let's get this one out there for anyone considering a big Semgrep rollout. We've been piloting it for a few months with a small team, and last week we finally enabled it for all ~100 developers across our microservices and platform repos. The goal was to shift-left on security and code quality, integrating it into our PR pipelines. We were using a mix of custom rules and the Semgrep Registry.
And, well... the initial blast radius was impressive 😅. Not in a catastrophic way, but we immediately hit some friction points I wish we'd stress-tested more.
**The Immediate Breakage:**
* **CI Pipeline Timeouts:** Our biggest issue. We added Semgrep as a step in our existing GitHub Actions workflows. For some of our larger monorepos (think 500k+ lines of code), the default scan with a moderate rule set (20-25 rules) started hitting the 60-minute job timeout. The semgrep-agent approach with `--baseline-ref` helped on subsequent runs, but that first scan on the main branch was a killer.
```yaml
# This choked on big repos
- name: Semgrep Scan
run: |
semgrep scan --config auto --error
```
**Fix:** We had to implement a tiered rollout by repo size and adjust timeouts. For the biggest repos, we started with a minimal, critical-security-only rule subset.
* **False Positive Firestorm:** We naively enabled the full `python.security` and `python.best-practice` bundles from the Registry. This generated *thousands* of findings, mostly for patterns that are intentional in our codebase (e.g., deliberate use of `assert` in non-production code, certain "wildcard imports" in Django settings). The noise immediately eroded developer trust. Our Slack channel was flooded with "Do I really need to fix this?" messages.
* **Configuration Collision Chaos:** We have a mix of projects using `.semgrep.yml` at the project root *and* a central CI configuration defining rules. The precedence wasn't clear to everyone, and we had cases where a developer's local `.semgrep.yml` (maybe an older version) was suppressing a rule that CI was now enforcing, causing "why did this pass locally but fail in CI?" confusion.
**What We Learned / How We're Adapting:**
* **Start Extremely Narrow:** Begin with a **tiny**, high-signal rule set. We rolled back to literally 5 rules covering critical security issues (like hardcoded secrets, SQL injection patterns). Once that's stable, grow slowly.
* **Communicate the "Why" for Each Rule:** We're now using `semgrep --config` with a custom rules repo, and each rule has a detailed `message:` field linking to our internal wiki page explaining the risk and the fix.
* **Tune Aggressively:** We're making heavy use of `paths:` to include/exclude and pattern filters (`pattern-not:`) to silence known, accepted patterns in our codebase. It's a bit of upkeep, but it's necessary.
* **Local Scan First:** We're pushing developers to run `semgrep ci` locally before pushing, which simulates the CI environment and uses the same config. This has reduced surprise failures.
It's a powerful tool, and we're sticking with it, but the "big bang" enablement was a lesson in incremental rollout. The key is treating it like any new platform service: you need gradual exposure, clear docs, and a feedback loop.
Has anyone else hit similar scaling or noise walls? How did you structure your rule rollout to keep devs on board?
bw
Automate all the things.
Predictable. The timeout issue is a classic vanity metric trap - scanning for the sake of saying you scan.
Did you actually measure the signal-to-noise ratio on those 20-25 rules before rollout? In my experience, at least a third of the registry rules are low-severity noise that just pisses off devs and clogs the pipeline. You end up tuning them out.
The tiered rollout is just process masking a product problem. You need to ruthlessly prune the rule set first, prove it catches real bugs without the false positives, then scale.
If it's not a retention curve, I don't care.