SyncVals · Trajectory

s3-lambda-ddb-pipeline

claude-code claude-opus-4-7 ✗ failed BAD_FAILURE ↑ View task

Solved from the instruction alone, tests/ and solution/ were withheld from the agent's workspace and restored only for grading.

Reward = tests/test.sh exit code (0 → resolved); the classification below is post-hoc and cannot change it.

Classification , post-hoc; cannot change the reward

BAD_FAILUREThe task is at fault, underspecified/contradictory instruction, brittle/flaky tests, or tests demanding undiscoverable behavior.

SubtypeUnderspecified Instruction

EvidenceTest failure: `test_end_to_end_put_creates_ddb_item` , key='verifier/red flower-506c443e26644f87805e16295afabd74.bin' never matches DynamoDB item. Agent's self-test with 'selftest-1776798064.txt' (no special chars) passed, but verifier test with space-containing key failed. Lambda handler stores raw `key = s3.get('object', {}).get('key', '')` without URL-decoding. Task description warns: 'Most failures come from forgetting to URL-decode the S3 event payload's object key (`%20` / `+` for space).'

Root causeThe instruction requires writing 'the S3 object key' to DynamoDB but doesn't explicitly mention URL-decoding the event payload's key field. S3 sends object keys URL-encoded in events (spaces become %20), and the agent stored the encoded form instead of decoding it, causing keys with special characters to not match the verifier's lookup.

RecommendationUpdate instruction requirement 5 to explicitly state: 'The `object_key` attribute must be the **URL-decoded** S3 object key from the event payload (S3 events send keys with URL encoding like %20 for spaces).' Alternatively, add this requirement as a separate item (e.g., 'The Lambda must URL-decode the `object_key` field from the S3 event before storing it') to make it unmissably clear, given the task.toml already identifies this as the 'classic' failure mode.

Trajectory

Tool-by-tool agent trajectory

7 tool calls · 2 tool types · 11 steps

# S3 -> Lambda -> DynamoDB event pipeline ## Environment - **AWS endpoint:** LocalStack at `http://localstack:4566`. All AWS SDKs and CLIs in this environment already honour the pre-exported `AWS_ENDPOINT_URL=http://localstack:4566`. - **Credentials & region:** `AWS_ACCESS_KEY_ID=test`, `AWS_SECRET_ACCESS_KEY=test`, `AWS_DEFAULT_REGION=us-east-1`. Account ID is `000000000000` (LocalStack's default), which is the value to use when constructing ARNs. - **Installed tools:** `aws` (AWS CLI v2), `awslocal` (pre-configured for LocalStack), `python3`, `boto3`, `curl`, `jq`, `git`, `unzip`, `zip`. A Python venv at `/opt/venv` with `boto3` and `awscli-local` is already on `PATH`. - **Lambda networking:** Lambda functions created in this environment run in Docker containers on the same Compose network as LocalStack and can reach it at `http://localstack:4566`. The function's own `AWS_ENDPOINT_URL` must be set to that value for SDK calls from inside the function to hit LocalStack rather than real AWS. - **Working directory:** `/app`. It is empty , there are no starter files, templates, handlers, hints, or secrets. Everything the pipeline needs must be authored by you. ## Task Build the pipeline described below from scratch and deploy it via **CloudFormation** , the grader rejects solutions built imperatively with the CLI or SDK. The end state must be produced by at least one CloudFormation stack named **`pipeline-stack`** that owns the S3 bucket, the DynamoDB table, and the Lambda function. You are free to split into multiple stacks, add custom resources, choose any logical IDs, and use either `Code.ZipFile` or `Code.S3Bucket` for the Lambda code. ## Required outcome After you finish, the following must all be true in the LocalStack account: 1. A CloudFormation stack named **`pipeline-stack`** exists in `CREATE_COMPLETE` or `UPDATE_COMPLETE` and its stack resources include the S3 bucket `pipeline-source`, the DynamoDB table `pipeline-events`, and the Lambda function `pipeline-processor`. 2. An S3 bucket named **`pipeline-source`** exists. 3. A DynamoDB table named **`pipeline-events`** exists with a single string partition key `object_key`. 4. A Lambda function named **`pipeline-processor`** exists (runtime `python3.11`) and is invoked whenever an object is created in `pipeline-source`. 5. When a new object is put into `pipeline-source`, the Lambda must write one item to `pipeline-events` with these attributes: - `object_key` (S) , the S3 object key - `bucket` (S) , the source bucket name - `size` (N) , the object size in bytes - `event_time` (S) , the S3 event timestamp (non-empty) 6. The Lambda must have permission to be invoked by the S3 service (`Principal: s3.amazonaws.com`) for events from `pipeline-source`. 7. The Lambda execution role must have `dynamodb:PutItem` permission on the `pipeline-events` table. 8. The `pipeline-events` table must be encrypted at rest with a **customer-managed** KMS CMK that is itself created by the `pipeline-stack` CloudFormation stack (not the AWS-managed `alias/aws/dynamodb` key). 9. The Lambda execution role must be able to use that CMK , its policy set must grant `kms:Decrypt` and `kms:GenerateDataKey` on the CMK's ARN (or with `Resource: "*"`). Without these, the Lambda's `PutItem` would fail against an encrypted table even though `dynamodb:PutItem` is granted. ## End-to-end grading The grader uploads a fresh object to `pipeline-source` with a key it chooses, then polls `pipeline-events` for an item whose `object_key` equals that same key. If the item does not appear within a reasonable timeout, the task fails. The grader does not trust any agent-written tests; all assertions run out-of-band against the live LocalStack account.

Check working directory and tool versions

shell

ls -la && echo "---" && aws --version && echo "---" && awslocal --version 2>&1 | head -5

output

total 8
drwxr-xr-x 2 root root 4096 Apr 21 17:23 .
drwxr-xr-x 1 root root 4096 Apr 21 18:57 ..
---
aws-cli/2.34.33 Python/3.14.4 Linux/6.10.14-linuxkit exe/aarch64.ubuntu.24
---
aws-cli/2.34.33 Python/3.14.4 Linux/6.10.14-linuxkit exe/aarch64.ubuntu.24

[stdout]
total 8
drwxr-xr-x 2 root root 4096 Apr 21 17:23 .
drwxr-xr-x 1 root root 4096 Apr 21 18:57 ..
---
aws-cli/2.34.33 Python/3.14.4 Linux/6.10.14-linuxkit exe/aarch64.ubuntu.24
---
aws-cli/2.34.33 Python/3.14.4 Linux/6.10.14-linuxkit exe/aarch64.ubuntu.24

Verify LocalStack connectivity and current stacks

shell

awslocal sts get-caller-identity && echo "---" && awslocal cloudformation list-stacks --query 'StackSummaries[].[StackName,StackStatus]' --output table 2>&1 | head -20

output

{
    "UserId": "AKIAIOSFODNN7EXAMPLE",
    "Account": "000000000000",
    "Arn": "arn:aws:iam::000000000000:root"
}
---

[stdout]
{
    "UserId": "AKIAIOSFODNN7EXAMPLE",
    "Account": "000000000000",
    "Arn": "arn:aws:iam::000000000000:root"
}
---

I'll build this from scratch: a CloudFormation template with the KMS CMK, DynamoDB table, Lambda with inline code, IAM role, Lambda permission, and S3 bucket with notification config. Let me write it now.

write · /app/pipeline-stack.yaml

AWSTemplateFormatVersion: '2010-09-09'
Description: S3 -> Lambda -> DynamoDB event pipeline

Resources:
  PipelineKey:
    Type: AWS::KMS::Key
    Properties:
      Description: Customer-managed CMK for pipeline-events table
      EnableKeyRotation: true
      KeyPolicy:
        Version: '2012-10-17'
        Statement:
          - Sid: EnableRootPermissions
            Effect: Allow
            Principal:
              AWS: !Sub arn:aws:iam::${AWS::AccountId}:root
            Action: kms:*
            Resource: '*'

  EventsTable:
    Type: AWS::DynamoDB::Table
    Properties:
      TableName: pipeline-events
      BillingMode: PAY_PER_REQUEST
      AttributeDefinitions:
        - AttributeName: object_key
          AttributeType: S
      KeySchema:
        - AttributeName: object_key
          KeyType: HASH
      SSESpecification:
        SSEEnabled: true
        SSEType: KMS
        KMSMasterKeyId: !GetAtt PipelineKey.Arn

  ProcessorRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: pipeline-processor-inline
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
              - Effect: Allow
                Action:
                  - dynamodb:PutItem
                Resource: !GetAtt EventsTable.Arn
              - Effect: Allow
                Action:
                  - kms:Decrypt
                  - kms:GenerateDataKey
                Resource: !GetAtt PipelineKey.Arn

  Processor:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: pipeline-processor
      Runtime: python3.11
      Handler: index.handler
      Role: !GetAtt ProcessorRole.Arn
      Timeout: 30
      Environment:
        Variables:
          AWS_ENDPOINT_URL: http://localstack:4566
          TABLE_NAME: !Ref EventsTable
      Code:
        ZipFile: |
          import os
          import boto3

          _endpoint = os.environ.get('AWS_ENDPOINT_URL') or None
          ddb = boto3.client('dynamodb', endpoint_url=_endpoint)
          TABLE = os.environ['TABLE_NAME']

          def handler(event, context):
              for record in event.get('Records', []):
                  s3 = record.get('s3', {})
                  bucket = s3.get('bucket', {}).get('name', '')
                  key = s3.get('object', {}).get('key', '')
                  size = s3.get('object', {}).get('size', 0)
                  event_time = record.get('eventTime') or ''
                  ddb.put_item(
                      TableName=TABLE,
                      Item={
                          'object_key': {'S': key},
                          'bucket': {'S': bucket},
                          'size': {'N': str(int(size))},
                          'event_time': {'S': str(event_time)},
                      },
                  )
              return {'ok': True}

  InvokePermission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !GetAtt Processor.Arn
      Action: lambda:InvokeFunction
      Principal: s3.amazonaws.com
      SourceAccount: !Ref AWS::AccountId
      SourceArn: arn:aws:s3:::pipeline-source

  SourceBucket:
    Type: AWS::S3::Bucket
    DependsOn: InvokePermission
    Properties:
      BucketName: pipeline-source
      NotificationConfiguration:
        LambdaConfigurations:
          - Event: s3:ObjectCreated:*
            Function: !GetAtt Processor.Arn

Outputs:
  BucketName:
    Value: !Ref SourceBucket
  TableName:
    Value: !Ref EventsTable
  FunctionName:
    Value: !Ref Processor
  KmsKeyArn:
    Value: !GetAtt PipelineKey.Arn

Create the pipeline-stack CloudFormation stack

shell

awslocal cloudformation create-stack --stack-name pipeline-stack --template-body file://pipeline-stack.yaml --capabilities CAPABILITY_IAM 2>&1

output

{
    "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/pipeline-stack/cee82c40-b88f-4bf9-a99d-9f92bda7f7f8"
}

[stdout]
{
    "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/pipeline-stack/cee82c40-b88f-4bf9-a99d-9f92bda7f7f8"
}

Wait for stack create completion

shell

awslocal cloudformation wait stack-create-complete --stack-name pipeline-stack 2>&1 && echo "OK" && awslocal cloudformation describe-stacks --stack-name pipeline-stack --query 'Stacks[0].StackStatus' --output text

output

OK
CREATE_COMPLETE

[stdout]
OK
CREATE_COMPLETE

Stack created. Now let me verify all resources and test end-to-end.

Verify deployed resources

shell

echo "=== Stack resources ===" && awslocal cloudformation list-stack-resources --stack-name pipeline-stack --query 'StackResourceSummaries[].[LogicalResourceId,ResourceType,ResourceStatus]' --output table
echo "=== Bucket ==="
awslocal s3 ls | grep pipeline-source
echo "=== Table ==="
awslocal dynamodb describe-table --table-name pipeline-events --query 'Table.[TableName,KeySchema,AttributeDefinitions,SSEDescription]'
echo "=== Lambda ==="
awslocal lambda get-function --function-name pipeline-processor --query 'Configuration.[FunctionName,Runtime,Handler]'
echo "=== Bucket notification ==="
awslocal s3api get-bucket-notification-configuration --bucket pipeline-source

output

=== Stack resources ===
--------------------------------------------------------------------
|                        ListStackResources                        |
+------------------+---------------------------+-------------------+
|  PipelineKey     |  AWS::KMS::Key            |  CREATE_COMPLETE  |
|  EventsTable     |  AWS::DynamoDB::Table     |  CREATE_COMPLETE  |
|  ProcessorRole   |  AWS::IAM::Role           |  CREATE_COMPLETE  |
|  Processor       |  AWS::Lambda::Function    |  CREATE_COMPLETE  |
|  InvokePermission|  AWS::Lambda::Permission  |  CREATE_COMPLETE  |
|  SourceBucket    |  AWS::S3::Bucket          |  CREATE_COMPLETE  |
+------------------+---------------------------+-------------------+
=== Bucket ===
2026-04-21 19:00:19 pipeline-source
=== Table ===
[
    "pipeline-events",
    [
        {
            "AttributeName": "object_key",
            "KeyType": "HASH"
        }
    ],
    [
        {
            "AttributeName": "object_key",
            "AttributeType": "S"
        }
    ],
    {
        "Status": "ENABLED",
        "SSEType": "KMS",
        "KMSMasterKeyArn": "arn:aws:kms:us-east-1:000000000000:key/be91e8fd-ee81-4bd5-b92b-1fa329610a71"
    }
]
=== Lambda ===
[
    "pipeline-processor",
    "python3.11",
    "index.handler"
]
=== Bucket notification ===
{
    "LambdaFunctionConfigurations": [
        {
            "Id": "a426db5a",
            "LambdaFunctionArn": "arn:aws:lambda:us-east-1:000000000000:function:pipeline-processor",
            "Events": [
                "s3:ObjectCreated:*"
            ]
        }
    ]
}

[stdout]
=== Stack resources ===
--------------------------------------------------------------------
|                        ListStackResources                        |
+------------------+---------------------------+-------------------+
|  PipelineKey     |  AWS::KMS::Key            |  CREATE_COMPLETE  |
|  EventsTable     |  AWS::DynamoDB::Table     |  CREATE_COMPLETE  |
|  ProcessorRole   |  AWS::IAM::Role           |  CREATE_COMPLETE  |
|  Processor       |  AWS::Lambda::Function    |  CREATE_COMPLETE  |
|  InvokePermission|  AWS::Lambda::Permission  |  CREATE_COMPLETE  |
|  SourceBucket    |  AWS::S3::Bucket          |  CREATE_COMPLETE  |
+------------------+---------------------------+-------------------+
=== Bucket ===
2026-04-21 19:00:19 pipeline-source
=== Table ===
[
    "pipeline-events",
    [
        {
            "AttributeName": "object_key",
            "KeyType": "HASH"
        }
    ],
    [
        {
            "AttributeName": "object_key",
            "AttributeType": "S"
        }
    ],
    {
        "Status": "ENABLED",
        "SSEType": "KMS",
        "KMSMasterKeyArn": "arn:aws:kms:us-east-1:000000000000:key/be91e8fd-ee81-4bd5-b92b-1fa329610a71"
    }
]
=== Lambda ===
[
    "pipeline-processor",
    "python3.11",
    "index.handler"
]
=== Bucket notification ===
{
    "LambdaFunctionConfigurations": [
        {
            "Id": "a426db5a",
            "LambdaFunctionArn": "arn:aws:lambda:us-east-1:000000000000:function:pipeline-processor",
            "Events": [
                "s3:ObjectCreated:*"
            ]
        }
    ]
}

End-to-end test: upload S3 object, poll DynamoDB

shell

TEST_KEY="selftest-$(date +%s).txt"
echo "hello pipeline" > /tmp/test-obj.txt
awslocal s3 cp /tmp/test-obj.txt "s3://pipeline-source/$TEST_KEY"
echo "=== Uploaded key: $TEST_KEY ==="
for i in 1 2 3 4 5 6 7 8 9 10; do
  sleep 2
  RESULT=$(awslocal dynamodb get-item --table-name pipeline-events --key "{\"object_key\": {\"S\": \"$TEST_KEY\"}}" 2>&1)
  if echo "$RESULT" | grep -q '"Item"'; then
    echo "=== Found item after ${i}x2s ==="
    echo "$RESULT"
    break
  fi
  echo "attempt $i: not yet..."
done

output

Completed 15 Bytes/15 Bytes (1.7 KiB/s) with 1 file(s) remaining
upload: ../tmp/test-obj.txt to s3://pipeline-source/selftest-1776798064.txt
=== Uploaded key: selftest-1776798064.txt ===
=== Found item after 1x2s ===
{
    "Item": {
        "bucket": {
            "S": "pipeline-source"
        },
        "object_key": {
            "S": "selftest-1776798064.txt"
        },
        "size": {
            "N": "15"
        },
        "event_time": {
            "S": "2026-04-21T19:01:04.599Z"
        }
    }
}

[stdout]
Completed 15 Bytes/15 Bytes (1.7 KiB/s) with 1 file(s) remaining
upload: ../tmp/test-obj.txt to s3://pipeline-source/selftest-1776798064.txt
=== Uploaded key: selftest-1776798064.txt ===
=== Found item after 1x2s ===
{
    "Item": {
        "bucket": {
            "S": "pipeline-source"
        },
        "object_key": {
            "S": "selftest-1776798064.txt"
        },
        "size": {
            "N": "15"
        },
        "event_time": {
            "S": "2026-04-21T19:01:04.599Z"
        }
    }
}

Pipeline is fully working end-to-end. **Summary** - `pipeline-stack` is `CREATE_COMPLETE` and owns all six resources: KMS CMK, DynamoDB table, IAM role, Lambda, Lambda permission, S3 bucket. - `pipeline-source` bucket has an `s3:ObjectCreated:*` notification targeting `pipeline-processor`. - `pipeline-events` table has a string `object_key` partition key and is encrypted with the CMK from the same stack (SSEType `KMS`, CMK ARN shown above). - Lambda runtime is `python3.11` with `AWS_ENDPOINT_URL=http://localstack:4566` so its boto3 calls hit LocalStack. - Execution role grants `dynamodb:PutItem` on the table ARN and `kms:Decrypt`/`kms:GenerateDataKey` on the CMK ARN. - `InvokePermission` grants `lambda:InvokeFunction` to `s3.amazonaws.com` with `SourceArn: arn:aws:s3:::pipeline-source`. - Self-test: uploading a new object produced a DynamoDB item with `object_key`, `bucket`, `size=15`, and a non-empty `event_time` within ~2s. Template: `/app/pipeline-stack.yaml`.

Final diff , what the agent changed

No file changes, the agent left the workspace untouched.

Verifier output , the proof behind the reward

tests/test.sh

============================= test session starts ==============================
platform linux -- Python 3.12.3, pytest-8.4.1, pluggy-1.6.0 -- /root/.cache/uv/archive-v0/gBlcbhPZ1nQmIn_Zm11fa/bin/python
cachedir: .pytest_cache
rootdir: /tests
plugins: json-ctrf-0.3.5
collecting ... collected 13 items

../tests/test_state.py::test_aws_cli_binary_is_real PASSED               [  7%]
../tests/test_state.py::test_localstack_reachable PASSED                 [ 15%]
../tests/test_state.py::test_cfn_stack_is_deployed PASSED                [ 23%]
../tests/test_state.py::test_cfn_stack_owns_core_resources PASSED        [ 30%]
../tests/test_state.py::test_bucket_exists PASSED                        [ 38%]
../tests/test_state.py::test_table_exists_with_correct_schema PASSED     [ 46%]
../tests/test_state.py::test_lambda_exists_with_correct_runtime PASSED   [ 53%]
../tests/test_state.py::test_lambda_permission_allows_s3_invoke PASSED   [ 61%]
../tests/test_state.py::test_bucket_notification_points_at_lambda PASSED [ 69%]
../tests/test_state.py::test_stack_owns_customer_managed_kms_key PASSED  [ 76%]
../tests/test_state.py::test_ddb_encrypted_with_stack_cmk PASSED         [ 84%]
../tests/test_state.py::test_lambda_role_can_use_the_cmk PASSED          [ 92%]
../tests/test_state.py::test_end_to_end_put_creates_ddb_item FAILED      [100%]

=================================== FAILURES ===================================
_____________________ test_end_to_end_put_creates_ddb_item _____________________

s3 = <botocore.client.S3 object at 0xffff9fd02ea0>
ddb = <botocore.client.DynamoDB object at 0xffff9e94ed80>

    def test_end_to_end_put_creates_ddb_item(s3, ddb):
        key = f"verifier/red flower-{uuid.uuid4().hex}.bin"
        body = struct.pack(">Q", int(time.time_ns())) + os.urandom(32)
        s3.put_object(Bucket=BUCKET, Key=key, Body=body)
    
        deadline = time.time() + 60
        last_err = None
        item = None
        while time.time() < deadline:
            try:
                resp = ddb.get_item(
                    TableName=TABLE,
                    Key={"object_key": {"S": key}},
                    ConsistentRead=True,
                )
                if "Item" in resp:
                    item = resp["Item"]
                    break
            except ClientError as e:
                last_err = e
            time.sleep(1)
    
>       assert item is not None, (
            f"Lambda never wrote item for key={key} within 60s; last_err={last_err}"
        )
E       AssertionError: Lambda never wrote item for key=verifier/red flower-506c443e26644f87805e16295afabd74.bin within 60s; last_err=None
E       assert None is not None

/tests/test_state.py:297: AssertionError
=============================== warnings summary ===============================
test_state.py: 77 warnings
  /root/.cache/uv/archive-v0/gBlcbhPZ1nQmIn_Zm11fa/lib/python3.12/site-packages/botocore/auth.py:424: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
    datetime_now = datetime.datetime.utcnow()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
==================================== PASSES ====================================
=========================== short test summary info ============================
PASSED ../tests/test_state.py::test_aws_cli_binary_is_real
PASSED ../tests/test_state.py::test_localstack_reachable
PASSED ../tests/test_state.py::test_cfn_stack_is_deployed
PASSED ../tests/test_state.py::test_cfn_stack_owns_core_resources
PASSED ../tests/test_state.py::test_bucket_exists
PASSED ../tests/test_state.py::test_table_exists_with_correct_schema
PASSED ../tests/test_state.py::test_lambda_exists_with_correct_runtime
PASSED ../tests/test_state.py::test_lambda_permission_allows_s3_invoke
PASSED ../tests/test_state.py::test_bucket_notification_points_at_lambda
PASSED ../tests/test_state.py::test_stack_owns_customer_managed_kms_key
PASSED ../tests/test_state.py::test_ddb_encrypted_with_stack_cmk
PASSED ../tests/test_state.py::test_lambda_role_can_use_the_cmk
FAILED ../tests/test_state.py::test_end_to_end_put_creates_ddb_item - Asserti...
============= 1 failed, 12 passed, 77 warnings in 60.48s (0:01:00) =============

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_a679e0b040354aa4. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_a679e0b040354aa4 · verifier authoritative; classifier explanatory.