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fix(iac/aws): point Lambda at its own log group via logging_config - #354
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cristim
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Included review availability: This review used your included allowance. 0 included reviews remain after this review. Your included PR review attempts over the past 7 days set your current allowance at 5 reviews per hour. 📝 WalkthroughWalkthroughThe Lambda function now uses text-format CloudWatch logging directed to the module-managed log group. The log group name prefix uses the stack-based function name. A regression test checks the function and metric-filter references. ChangesLambda log group
Priority: ➖ Normal Estimated code review effort: 2 (Simple) | ~10 minutes Change: Bug fix · Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to Logs, retention, and migration monitoring are configured for the same group. The previously documented import obstacle no longer applies; no actionable merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Review comments at @terraform/modules/compute/aws/lambda/main.tf:
- Line 547: Update the import instructions for aws_cloudwatch_log_group.lambda
to explain that its existing state address must be freed by removing or moving
the old binding before importing the exact-named log group. Also instruct
operators to assess the old prefix-named group and clean it up if appropriate.
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terraform/modules/compute/aws/lambda/main.tfterraform/modules/compute/aws/lambda_log_group_test.go
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aws_lambda_function.main had no logging_config, so Lambda wrote to its
own auto-created /aws/lambda/<function_name> group regardless of what
aws_cloudwatch_log_group.lambda's name_prefix produced. That left
var.log_retention_days applied to an empty, unreferenced group while
production logs went to the auto-created group with "Never expire"
retention, and made the migration-failure metric filter
(migration-alarm.tf) attach to the same empty group, so it could never
fire on a failed migration.
An earlier revision of this fix changed the log group to an exact
name = "/aws/lambda/${var.stack_name}-api" to match the fixed name
Lambda writes to by default. That is wrong for this repo's actual
deployed state: the fixed-name group already exists in every
environment (Lambda auto-created it before this module ever managed a
log group), so Terraform creating a same-named resource fails with
ResourceAlreadyExistsException on the very next deploy (deploy-aws-lambda.yml
auto-applies on push to main). The previous revision's `terraform
import` runbook does not help either -- there is nothing to import
into for a resource address that was never in this module's state.
Fix (zero operator steps): keep aws_cloudwatch_log_group.lambda as
name_prefix (a distinct, Terraform-owned group, not the colliding fixed
name) and add logging_config { log_format = "Text", log_group =
aws_cloudwatch_log_group.lambda.name } to aws_lambda_function.main, so
Lambda writes to the group Terraform manages regardless of the group's
actual name. The log group's name_prefix stays the literal
"${var.stack_name}-api-" (not aws_lambda_function.main.function_name),
since the function now depends on the log group via logging_config and
a reference back the other way would cycle; dropped the depends_on
that literal used to need. requires aws provider >= 5.32 for
logging_config; this module's constraint (~> 5.0) already resolves to
5.100.0 per the committed lock file.
The old auto-created /aws/lambda/<stack>-api group is simply abandoned
by this change: its history is preserved, and it can be deleted
manually later once it's no longer needed for reference. No
ci-cd-permissions bootstrap re-apply and no manual import step is
required.
Regression test: terraform/modules/compute/aws/lambda_log_group_test.go
now asserts aws_cloudwatch_log_group.lambda uses name_prefix (not an
exact name, which would collide with the pre-existing group), that its
name_prefix is the literal "${var.stack_name}-api-", that
aws_lambda_function.main has a logging_config block referencing
aws_cloudwatch_log_group.lambda.name, and that the metric filter still
attaches to that same group. Verified it fails against the actual
current origin/main source (git show origin/main:.../lambda/main.tf
swapped in, test left in place) with the logging_config and
name_prefix-literal assertions both failing, and passes with this
fix restored.
Closes #126
Co-Authored-By: claude-flow <ruv@ruv.net>
8ac82d3 to
e3dcb64
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cristim
changed the title
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Independent adversarial review (two rounds) + local verification: MERGE at e3dcb64. Reworked to logging_config: the log group's name_prefix renders to the identical string (no state change, no import, no operator step); logging_config is an in-place UpdateFunctionConfiguration in provider v5.100.0 (only function_name/package_type force replacement); no cycle (validate passes); BasicExecutionRole already covers the managed group. Retention and the migration-failure metric filter now receive the function's logs; the old auto-created group keeps its history until deleted deliberately. Test fails on origin/main and passes (62/62); fmt/validate/tflint clean. Nit for a later touch: rename TestLambdaLogGroupUsesExactName to match what it now asserts. |
Summary
aws_lambda_function.mainhad nologging_config, so Lambda wrote to its own auto-created/aws/lambda/<function_name>group regardless of whataws_cloudwatch_log_group.lambda'sname_prefixproduced. That silently defeated both log retention and the migration-failure alarm.Root cause
/aws/lambda/${function_name}by default; withoutlogging_config, nothing tells it otherwise.terraform/modules/compute/aws/lambda/main.tfcreatedaws_cloudwatch_log_group.lambdawithname_prefix, producing a different, randomly-suffixed, always-empty group.var.log_retention_daysapplied to that empty group; real logs went to the auto-created group with "Never expire".aws_cloudwatch_log_metric_filter.migration_failed(migration-alarm.tf:33) attaches toaws_cloudwatch_log_group.lambda.name- the empty group - so it could never match anything withenable_migration_alarm = true.Revision note: reworked from an exact
nameAn earlier revision of this PR changed the log group to an exact
name = "/aws/lambda/${var.stack_name}-api", matching Lambda's default fixed name. That's wrong for this repo's actual deployed state: that fixed-name group already exists in every environment (Lambda auto-created it before this module ever managed one), so a same-named Terraform resource collides with it -ResourceAlreadyExistsExceptionon the next deploy, sincedeploy-aws-lambda.ymlauto-applies on push tomain. The previous revision'sterraform importrunbook doesn't help either: there's nothing to import into for a resource address that was never in this module's state.Fix (zero operator steps)
aws_cloudwatch_log_group.lambdaasname_prefix = "/aws/lambda/${var.stack_name}-api-"- a distinct, Terraform-owned group, not the colliding fixed name.logging_config { log_format = "Text", log_group = aws_cloudwatch_log_group.lambda.name }toaws_lambda_function.main, so Lambda writes to the group Terraform manages, whatever its actual (prefixed) name is.depends_onfrom the previous revision - thelogging_configreference is the dependency, andaws_cloudwatch_log_group.lambda'sname_prefixstays the literal${var.stack_name}-api-(notaws_lambda_function.main.function_name) specifically to avoid a cycle: the function now depends on the log group, so the log group referencing the function back would be circular.>= 5.32forlogging_config; this module's constraint (~> 5.0) already resolves to5.100.0per the committed lock file.The old auto-created
/aws/lambda/<stack>-apigroup is simply abandoned: its history is preserved, and it can be deleted manually later once no longer needed for reference.Regression test
terraform/modules/compute/aws/lambda_log_group_test.gonow asserts:aws_cloudwatch_log_group.lambdadoes not set an exactname(would collide with the pre-existing group).name_prefixis the literal"/aws/lambda/${var.stack_name}-api-".aws_lambda_function.mainhas alogging_configblock withlog_group = aws_cloudwatch_log_group.lambda.name.Proved it fails against the actual current
origin/mainsource (not just the pre-this-PR state):git show origin/main:terraform/modules/compute/aws/lambda/main.tfswapped in with the test left in place, thengo test ./terraform/modules/compute/aws/... -run TestLambdaLogGroupUsesExactName -v:Restoring the fix passes both.
Verification
go test ./terraform/...(GOWORK=off, repo root):okacross all packages.terraform fmt -check -diffonterraform/modules/compute/aws/lambda: clean.terraform init -backend=false && terraform validateinterraform/modules/compute/aws/lambdaandterraform/environments/aws: bothSuccess! The configuration is valid.tflint --config=.tflint.hcl --chdir=terraform/modules/compute/aws/lambda: no findings.plan/applywas run against real clouds, per policy.Notes
ci-cd-permissionsbootstrap re-apply is required; this is a runtime-module-only change and needs no manual import step, unlike the previous revision.Closes #126