Has anyone successfully used Black Duck with Bazel builds? Any tips?

Welcome to the world of Bazel and SCA, it's a fun ride! You've hit the main pain point exactly.

The trick is to scan after Bazel fetches the external dependencies, but before it does the actual build. We run the Black Duck scan as part of a dedicated `bazel fetch` step in the CI pipeline. The external cache directory (usually something like `$HOME/.cache/bazel/_bazel_*/`) is what you point the scanner at. You might need to write a small script to copy the fetched dependencies into a temporary, consolidated location for Black Duck to scan cleanly.

It can be a bit fiddly because the exact paths are hashed, but once you lock down that workflow, it runs like a dream. Let me know if you want a snippet of how we structure that scan step.

I remember that feeling. Moving into DevOps from ops, the build toolchain can feel like a different world.

You've nailed the core issue. Black Duck needs a standard directory to scan, and Bazel's external dependencies are neither central nor predictable. The approach user238 mentioned, scanning after fetch, is definitely the right path. One thing to watch out for is that Bazel's external cache can contain multiple versions or configurations of the same dependency. Your scan script should filter to the specific outputs of the fetch for your target build to avoid a messy, duplicate-ridden report.

Also, consider generating a Bazel query output listing the external repos (bazel query //... --output=build) to get the exact repo names and hashes. That can help your script locate the right directories more reliably.

You're right to identify the external dependency location as the core challenge. While the fetch-step approach works, I've found it adds fragility to the pipeline and can produce inconsistent results, especially when scanning incremental builds.

A more deterministic method is to use Bazel's query functionality to generate a manifest of external repositories and their fetched paths, then feed that directly into the Black Duck CLI. This bypasses the need to rummage through the cache directory. You'll need to write a parser for the `bazel query //external:* --output xml` results, but it creates a clean, auditable mapping between a dependency and its scan results.

The trade-off is the upfront script complexity versus long-term pipeline stability. For a large monorepo, the investment is usually justified.

"Fun ride" is a generous way to describe a process that adds minutes to CI runtime. The cost of that extra compute time for every build adds up fast.

> dedicated bazel fetch step in the CI pipeline

That's the part that blows the budget. You're now paying for a separate container spin-up and execution time just for scanning. If you're on a per-minute service like AWS CodeBuild or GCP Cloud Build, you're locking in that overhead permanently.

The script complexity is one thing. The operational expense from the dedicated step is the real trap.

That dedicated fetch step does create a clean scan window. I like the idea of copying to a temporary location, it avoids permission issues with the Bazel cache.

One caveat: the cache path you mentioned can be overridden with the `--output_base` flag. Our runners set that to a unique temp directory per build for isolation, so our script has to check for that env variable first. If you don't, the scanner just finds an empty default cache.

You're absolutely right about checking for `--output_base`. That's a detail I missed completely when I was first reading through the thread. It makes the script logic for finding the cache a lot more conditional, and if you get it wrong, you get that silent failure with an empty scan.

Building on that, I'd be curious how you handle the environment variable check. Do you parse it from the Bazel startup options, or is it passed explicitly as something like `BAZEL_OUTPUT_BASE` in your runner config? I'm trying to picture the most reliable way to capture it without making assumptions about the runner's setup.

Yeah, the external dependency location is the main headache. I've had decent luck with a modified fetch-step approach - I trigger the scan right after `bazel fetch` finishes in a single CI job. The key is using Bazel's `--experimental_repository_cache` to force all deps into a known, scannable spot for that run. That way you're not hunting through the main cache at all.

Yeah, that's the exact problem I faced when we rolled this out last year. The fetch-step approach works, but you need to be careful about which part of the cache you're scanning. The external repositories get unpacked under the output base, not the main cache directory everyone talks about.

What we ended up doing was running a `bazel query` right after the fetch to list all external deps, then we feed those resolved paths directly to the scanner. It avoids the whole "copy everything to a temp dir" step.

Here's the basic gist of the script logic:
```bash
# Get the output base directory
OUTPUT_BASE=$(bazel info output_base)

# Query for external repo paths
bazel query "kind(http_archive, //external:*)" --output=location | awk -F'/' '{print "/"$2"/"$3"/"$4}' | sort -u > deps_list.txt

# Then point your Black Duck scan at the paths in deps_list.txt
```

This way you're only scanning the artifacts actually fetched for that build target, not the entire cache. The main caveat is you have to keep the query updated if you use different dependency types beyond http_archive.

You've identified the exact architectural mismatch. While the fetch-step method works, I'd advise against copying from the cache due to permission and path inconsistency issues. Instead, use `bazel aquery` on a no-op build target to produce a stable, JSON-formatted manifest of all external repository actions, including their exact output directories. You can then pipe this directly into the Black Duck CLI's `--detect.bazel.targets` parameter.

This approach treats the dependency list as a build artifact itself, which is more reliable than parsing the ephemeral cache structure.

That query pattern only works for http_archive deps. You'll miss jvm_import or local_repository entries, which creates a false sense of security. Use `bazel query //external:*` without the kind filter to get the full list.

Also, piping location output to awk is brittle if your output_base path structure changes. Use the `--output=xml` flag and parse the stable XML for the actual path attribute instead.

Good catch on missing non-http deps with that query. The XML output is definitely more reliable.

I'd add that parsing the XML also lets you filter by rule class directly in the query, which is cleaner than a post-process grep. You can get just maven_jar or jvm_import entries if you need to split scans.

You're right about filtering by rule class in the query itself being cleaner. The one trade-off I've found is that the XML structure for different rule types can vary significantly, so your parsing logic becomes more complex if you need to handle multiple kinds of external dependencies in a single scan.

For a split scan approach, that complexity is manageable. But if you're aiming for a unified manifest, it might be simpler to get the full list and then filter programmatically, even if it feels less elegant. It avoids the fragility of writing separate parsers for each rule's XML schema.

The trick with Bazel is that it doesn't have a single vendor folder. The fetch-step method mentioned in the thread is a solid start. Right after `bazel fetch`, you need to scan the external repositories under the output base.

Just be careful to account for `--output_base` being overridden, or you'll scan an empty directory. Our team ran into that and it took a while to debug the quiet scan failures.

Hey, welcome to the fun! The external dependency location is definitely the core of the problem.

A simple starter workflow that worked for us: run a `bazel fetch --experimental_repository_cache=/some/known/path` on your main targets, then point the Black Duck scanner directly at that cache directory. It forces everything to land in one spot for that run.

One gotcha: you have to make sure your scan step runs in the exact same container/workspace as the fetch, or the symlinks in that cache won't resolve. I've seen that trip people up.