CI/CD Guide

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CI Pipeline Structure

The main workflow is .github/workflows/cicd-main.yml. It triggers on pushes to branches matching pull-request/[0-9]+ and deploy-release/*, on merge groups, on a daily schedule, and on manual dispatch.

is-not-external-contributor
  └─ pre-flight
       └─ configure          # determines scope, container tag, n_repeat
            ├─ linting
            ├─ cicd-container-build
            │    ├─ cicd-parse-unit-tests → cicd-unit-tests-latest
            │    ├─ cicd-parse-integration-tests-h100 → cicd-integration-tests-latest-h100
            │    └─ cicd-parse-integration-tests-gb200 → cicd-integration-tests-latest-gb200 (maintainers only)
            └─ Nemo_CICD_Test  # final pass/fail gate

Images are pushed to:

• AWS ECR: 766267172432.dkr.ecr.us-east-1.amazonaws.com/…
• GCP Artifact Registry: us-east4-docker.pkg.dev/nv-projdgxchipp-20260113193621/megatron-lm/…

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CI Test Scope Labels

The CI pipeline reads PR labels to decide test scope, n_repeat, and container image.

Decision tree (first match wins):

Orthogonal image label:

Which label to attach when opening a PR

Rule of thumb: default to Run tests. Always use Run functional tests when the PR adds new test cases (golden values must be generated) or when the change could plausibly shift loss curves.

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Triggering Internal CI

Use tools/trigger_internal_ci.py to push the current branch to the internal GitLab remote and trigger a pipeline — without touching the GitLab UI. Full setup and usage details: @tools/trigger_internal_ci.md.

Prerequisites (one-time):

# 1. Add the internal GitLab remote
git remote add gitlab git@<gitlab-hostname>:ADLR/Megatron-LM.git

# 2. Create a personal access token with 'api' scope on your GitLab profile,
#    then store it:
export GITLAB_TOKEN=glpat-<your-token>

Usage:

python tools/trigger_internal_ci.py \
  --gitlab-origin gitlab \
  [--functional-test-scope mr] \
  [--functional-test-repeat 5] \
  [--functional-test-cases all] \
  [--dry-run]

The script force-pushes the current branch as pull-request/<branch> and prints the resulting pipeline URL.

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CI Failure Investigation

CI branches always follow the pattern pull-request/<number>.

Locating the PR from a CI Branch

# Extract PR number from the current branch
PR_NUMBER=$(git rev-parse --abbrev-ref HEAD | grep -oP '(?<=pull-request/)\d+')

# Fetch the PR metadata (title, labels, author, base branch)
gh pr view "$PR_NUMBER" --repo NVIDIA/Megatron-LM

# Show the changeset for that PR
gh pr diff "$PR_NUMBER" --repo NVIDIA/Megatron-LM

Reading CI Job Logs

# List recent workflow runs for the PR
gh run list --repo NVIDIA/Megatron-LM --branch "pull-request/$PR_NUMBER"

# Stream failing job output
gh run view <run-id> --repo NVIDIA/Megatron-LM --log-failed

Full per-rank logs are not in the runner stdout. They are uploaded as GitHub artifacts named logs-<test_case>-<run_id>-<uuid>.

# 1. Find artifact name
gh run view <run-id> --repo NVIDIA/Megatron-LM --json artifacts \
  --jq '.artifacts[].name'

# 2. Download the artifact zip
gh run download <run-id> --repo NVIDIA/Megatron-LM \
  --name "logs-<artifact-name>" -D ./ci-logs

# 3. Locate which rank logs contain errors
grep -r -l "ERROR\|Traceback\|FAILED\|fatal" ./ci-logs/

# 4. Log files can exceed 10 000 lines — never read a full log at once.
wc -l ./ci-logs/<test>/<attempt>/attempt_0/<rank>/stderr.log
sed -n '1,200p' ./ci-logs/.../stderr.log   # read in chunks

Identifying Failure Root Cause

1. Linting failure — re-run tools/autoformat.sh locally; the diff shows exactly what needs to change.
2. Container build failure — inspect the cicd-container-build job log.
3. Unit test failure — the failing bucket is in the cicd-unit-tests-latest job matrix.
4. Functional test failure — look at the cicd-integration-tests-* job. Start with stdout.log for rank 0.
5. Flaky test — the runner retries automatically up to 3 times. If all retries exhausted and the pattern matches a known transient (NCCL, ECC, segfault), it is infrastructure noise.

Correlating a Failure with the PR Changeset

# Find unit tests that cover a changed source file
grep -r "from megatron.core.transformer.attention" tests/unit_tests/ -l

# Check CODEOWNERS for reviewer assignment
cat .github/CODEOWNERS | grep "<changed-path>"