To troubleshoot a VMware Tanzu buildpack failure, find the first failing lifecycle phase, capture the full build log, and identify the buildpack IDs and versions involved. Then check detection and buildpack order, execution errors, platform limits, and whether the buildpack or application code is within the supported support boundary. A final “build failed” line alone does not identify the cause.
Start by locating the failing build phase
Record the product and release, workload or application identifier, builder or stack, buildpack IDs and versions, and the complete build output. Focus on the first error and the lifecycle phase where it occurs—detection, build, or export/install—rather than treating the last failure message as a diagnosis.
For a Tanzu Application Platform (TAP) workload using Tanzu Build Service (TBS), Broadcom recommends setting BP_LOG_LEVEL=DEBUG in workload.yaml to obtain more verbose buildpack logs. See Broadcom’s guidance for enabling buildpack debug logs.
Classify what the output shows before changing configuration:
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- A detection status or “no app detected” message points to detection, source contents, or buildpack selection.
- An error after detection points to buildpack execution or a later lifecycle phase; use the earliest error to narrow the investigation.
- An HTTP 413 during installation of a large Java CNB may indicate a staged-size limit; verify the product version and the exact error before changing a limit.
Understand detector status 20 and 21
The Cloud Native Buildpacks lifecycle assigns different meanings to these detector exit statuses: status 20 means every buildpack group failed detection without an error; status 21 means every group failed detection and at least one buildpack errored. The distinction helps locate the problem in detection, but neither status by itself identifies a fix. See the lifecycle specification.
When detection fails cleanly
Check that the source tree contains the manifest, lockfile, or configuration files the selected buildpack expects, and that the application meets that buildpack’s language or framework detection requirements. Requirements vary by buildpack, so do not assume that a file or convention required by one language buildpack applies to another.
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When a detector errors
Look for the detector’s own error details in the log and distinguish an actual detector error from a clean “not applicable” result. Status 21 indicates at least one group encountered a detector error, but the log is needed to identify which buildpack and why.
Check buildpack selection and order
A buildpack can fail to detect an app because it is being evaluated in an incompatible order or because a different buildpack is a better match. Broadcom documents a Tanzu Application Service (TAS) 4.0+ example in which a Notifications UI errand returned detector status 20 and NoAppDetectedError: a web servers CNB was above the Go buildpack in the buildpack list, so the Go app was being matched against the web servers CNB. The documented correction was to move the Go buildpack above the web servers entry with cf update-buildpack. Details are in Broadcom’s TAS example.
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This is one documented case, not a general remedy for every status 20. Before changing order, confirm the app’s framework and the buildpacks configured for the relevant application or platform.
Identify which ClusterBuildpack ran in TAP or TBS
For a TAP/TBS build, use the build output to establish which buildpack IDs and versions participated, then match that metadata to installed ClusterBuildpack resources. TAP does not show the originating ClusterBuildpack directly in the build plan, so matching the log metadata is important when resource names are ambiguous or multiple versions are installed.
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- Capture the build output with
kp build logs <image-name>. - Note the participating buildpack IDs and versions in the log.
- List available resources with
kubectl get clusterbuildpacks. - Inspect candidate metadata with
kubectl describe clusterbuildpack <name>and compare it with the IDs and versions from the log.
Broadcom outlines this log-to-resource matching approach in its ClusterBuildpack identification guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check staged-size limits for HTTP 413 errors
If installing a large Java CNB fails with HTTP 413, check the configured Maximum staged droplet size. Broadcom says the default is 8 GB in Tanzu Platform 10.3.0 or later; its article recommends manually increasing the setting when an older or modified configuration is too low. The 8 GB figure is specific to that product version and setting, not a universal Tanzu limit. Confirm that the error is the staged-size upload problem and that the installed version matches before adjusting the limit. See Broadcom’s staged-size guidance.
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Verify dependency-update and installation changes
Broadcom published a Tanzu Build Service installation and automatic dependency-update process change scheduled for January 26, 2026. The notice includes migration requirements for some users and a change to how dependencies are obtained. If a build fails because a build resource is missing, outdated, or mismatched, check whether the migration applies to your installation and consult the release documentation for its version. The notice does not establish that the process change causes every build failure. Review Broadcom’s process-change notice.
Prepare a useful support escalation
Broadcom’s published support scope includes failed-build troubleshooting when the issue is within TBS, kpack, or a supported Tanzu/Paketo CNB, as well as help with supported buildpack packaging. Its examples of out-of-scope issues include debugging custom application code and custom or forked buildpacks. Check current entitlement and policy before assuming a case is covered; see Broadcom’s support scope.
Quick Recap
Include the following evidence in an escalation:
- Complete, reproducible build logs and the first failing lifecycle phase.
- Exact Tanzu product and release versions, workload or application identifier, and builder or stack.
- Participating buildpack IDs and versions, plus relevant ClusterBuildpack metadata for TAP/TBS.
- The configuration or recent process changes relevant to the failure, such as buildpack order, staged-size limits, or an applicable dependency-update migration.
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