SyncVals · Trajectory

s3-lambda-ddb-pipeline

claude-code claude-opus-4-7 ✓ resolved GOOD_SUCCESS ↑ 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

GOOD_SUCCESSLegitimate solve, implements the asked-for behavior; tests verify real functionality.

SubtypeLegitimate Solution

EvidenceAll 13 tests passed including: test_cfn_stack_is_deployed, test_stack_owns_customer_managed_kms_key, test_ddb_encrypted_with_stack_cmk, test_lambda_role_can_use_the_cmk, and test_end_to_end_put_creates_ddb_item. The agent created a CloudFormation template that correctly: (1) creates a customer-managed KMS CMK with proper key policy, (2) sets up DynamoDB table with KMS encryption, (3) creates Lambda function that URL-decodes S3 object keys (the documented #1 failure mode), (4) grants both dynamodb:PutItem AND kms:Decrypt/GenerateDataKey to the Lambda role, (5) breaks the S3↔Lambda circular dependency with DependsOn and hardcoded SourceArn, and (6) verifies end-to-end that uploading an object produces the expected DynamoDB item with all four attributes (object_key, bucket, size, event_time).

Root causeThe agent correctly understood and implemented all requirements from the comprehensive instruction, including the complex CloudFormation patterns (KMS key policies, IAM role permissions, S3 notification circular dependency) and the critical URL-decoding detail for S3 object keys.

RecommendationN/A - task is fine

Trajectory

Tool-by-tool agent trajectory

8 tool calls · 2 tool types · 12 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 AWS identity

shell

ls -la /app && echo "---" && awslocal sts get-caller-identity

output

total 8
drwxr-xr-x 2 root root 4096 Apr 21 17:23 .
drwxr-xr-x 1 root root 4096 Apr 21 19:05 ..
---
{
    "UserId": "AKIAIOSFODNN7EXAMPLE",
    "Account": "000000000000",
    "Arn": "arn:aws:iam::000000000000:root"
}

[stdout]
total 8
drwxr-xr-x 2 root root 4096 Apr 21 17:23 .
drwxr-xr-x 1 root root 4096 Apr 21 19:05 ..
---
{
    "UserId": "AKIAIOSFODNN7EXAMPLE",
    "Account": "000000000000",
    "Arn": "arn:aws:iam::000000000000:root"
}

List existing CloudFormation stacks

shell

awslocal cloudformation list-stacks --query 'StackSummaries[].{Name:StackName,Status:StackStatus}' 2>&1 | head -40

output

[]

[stdout]
[]

I'll build this pipeline. Let me first outline the plan, then write the CloudFormation template. The main challenge is the classic S3→Lambda circular dependency in CloudFormation: the bucket's notification config references the Lambda, but the Lambda permission needs the bucket ARN. I'll break it by hardcoding the bucket name in the `SourceArn` (safe since the name is fixed) and using `DependsOn` to order resource creation.

write · /app/template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Description: S3 -> Lambda -> DynamoDB 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: '*'
          - Sid: AllowDynamoDB
            Effect: Allow
            Principal:
              Service: dynamodb.amazonaws.com
            Action:
              - kms:Decrypt
              - kms:Encrypt
              - kms:GenerateDataKey
              - kms:DescribeKey
            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: !Ref PipelineKey

  LambdaRole:
    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: PipelineAccess
          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

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

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

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

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

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

Outputs:
  BucketName:
    Value: !Ref SourceBucket
  TableName:
    Value: !Ref EventsTable
  FunctionName:
    Value: !Ref ProcessorFunction
  KeyArn:
    Value: !GetAtt PipelineKey.Arn

Validate CloudFormation template

shell

awslocal cloudformation validate-template --template-body file://template.yaml 2>&1

output

{
    "Parameters": [],
    "Description": "S3 -> Lambda -> DynamoDB pipeline"
}

[stdout]
{
    "Parameters": [],
    "Description": "S3 -> Lambda -> DynamoDB pipeline"
}

Create pipeline-stack

shell

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

output

{
    "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/pipeline-stack/4da89861-ca01-4f77-a0d0-b3e87b38aaa3"
}

[stdout]
{
    "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/pipeline-stack/4da89861-ca01-4f77-a0d0-b3e87b38aaa3"
}

Poll stack status

shell

for i in 1 2 3 4 5 6 7 8 9 10; do status=$(awslocal cloudformation describe-stacks --stack-name pipeline-stack --query 'Stacks[0].StackStatus' --output text 2>&1); echo "try $i: $status"; case "$status" in CREATE_COMPLETE|UPDATE_COMPLETE|*FAILED*|*ROLLBACK*) break ;; esac; sleep 3; done

output

try 1: CREATE_IN_PROGRESS
try 2: CREATE_COMPLETE

[stdout]
try 1: CREATE_IN_PROGRESS
try 2: CREATE_COMPLETE

List stack resources

shell

awslocal cloudformation list-stack-resources --stack-name pipeline-stack --query 'StackResourceSummaries[].{L:LogicalResourceId,P:PhysicalResourceId,T:ResourceType,S:ResourceStatus}' --output table 2>&1

output

----------------------------------------------------------------------------------------------------------------------------
|                                                    ListStackResources                                                    |
+------------------------+--------------------------------------------------+------------------+---------------------------+
|            L           |                        P                         |        S         |             T             |
+------------------------+--------------------------------------------------+------------------+---------------------------+
|  PipelineKey           |  2d8b7c50-e66b-40ef-ab65-bc2eaea17ec6            |  CREATE_COMPLETE |  AWS::KMS::Key            |
|  EventsTable           |  pipeline-events                                 |  CREATE_COMPLETE |  AWS::DynamoDB::Table     |
|  LambdaRole            |  pipeline-stack-LambdaRole-71caf43b              |  CREATE_COMPLETE |  AWS::IAM::Role           |
|  ProcessorFunction     |  pipeline-processor                              |  CREATE_COMPLETE |  AWS::Lambda::Function    |
|  LambdaInvokePermission|  pipeline-stack-LambdaInvokePermission-dba1ec4d  |  CREATE_COMPLETE |  AWS::Lambda::Permission  |
|  SourceBucket          |  pipeline-source                                 |  CREATE_COMPLETE |  AWS::S3::Bucket          |
+------------------------+--------------------------------------------------+------------------+---------------------------+

[stdout]
----------------------------------------------------------------------------------------------------------------------------
|                                                    ListStackResources                                                    |
+------------------------+--------------------------------------------------+------------------+---------------------------+
|            L           |                        P                         |        S         |             T             |
+------------------------+--------------------------------------------------+------------------+---------------------------+
|  PipelineKey           |  2d8b7c50-e66b-40ef-ab65-bc2eaea17ec6            |  CREATE_COMPLETE |  AWS::KMS::Key            |
|  EventsTable           |  pipeline-events                                 |  CREATE_COMPLETE |  AWS::DynamoDB::Table     |
|  LambdaRole            |  pipeline-stack-LambdaRole-71caf43b              |  CREATE_COMPLETE |  AWS::IAM::Role           |
|  ProcessorFunction     |  pipeline-processor                              |  CREATE_COMPLETE |  AWS::Lambda::Function    |
|  LambdaInvokePermission|  pipeline-stack-LambdaInvokePermission-dba1ec4d  |  CREATE_COMPLETE |  AWS::Lambda::Permission  |
|  SourceBucket          |  pipeline-source                                 |  CREATE_COMPLETE |  AWS::S3::Bucket          |
+------------------------+--------------------------------------------------+------------------+---------------------------+

All resources created. Now let me verify the end-to-end flow by uploading an object and checking DynamoDB.

Upload test object and scan DynamoDB

shell

echo "hello world content" > /tmp/testobj.txt && awslocal s3api put-object --bucket pipeline-source --key test/obj-$(date +%s).txt --body /tmp/testobj.txt 2>&1 | tail -5
sleep 4
awslocal dynamodb scan --table-name pipeline-events 2>&1

output

"ETag": "\"9e08097211313f1728e5c0551442f244\"",
    "ChecksumCRC64NVME": "hXdPani1qNg=",
    "ChecksumType": "FULL_OBJECT",
    "ServerSideEncryption": "AES256"
}
{
    "Items": [
        {
            "bucket": {
                "S": "pipeline-source"
            },
            "object_key": {
                "S": "test/obj-1776798468.txt"
            },
            "size": {
                "N": "20"
            },
            "event_time": {
                "S": "2026-04-21T19:07:49.155Z"
            }
        }
    ],
    "Count": 1,
    "ScannedCount": 1,
    "ConsumedCapacity": null
}

[stdout]
    "ETag": "\"9e08097211313f1728e5c0551442f244\"",
    "ChecksumCRC64NVME": "hXdPani1qNg=",
    "ChecksumType": "FULL_OBJECT",
    "ServerSideEncryption": "AES256"
}
{
    "Items": [
        {
            "bucket": {
                "S": "pipeline-source"
            },
            "object_key": {
                "S": "test/obj-1776798468.txt"
            },
            "size": {
                "N": "20"
            },
            "event_time": {
                "S": "2026-04-21T19:07:49.155Z"
            }
        }
    ],
    "Count": 1,
    "ScannedCount": 1,
    "ConsumedCapacity": null
}

Pipeline is live and working end-to-end. The item landed in `pipeline-events` with all four required attributes populated correctly. **Summary of what was built** (`/app/template.yaml`, stack `pipeline-stack`): - `AWS::KMS::Key` (customer-managed CMK) with policy allowing root and DynamoDB service - `AWS::DynamoDB::Table` `pipeline-events`, partition key `object_key` (S), SSE-KMS using the CMK - `AWS::IAM::Role` for Lambda with `dynamodb:PutItem` on the table and `kms:Decrypt`/`GenerateDataKey` on the CMK - `AWS::Lambda::Function` `pipeline-processor` (python3.11, inline `ZipFile`) that parses S3 records and writes items - `AWS::Lambda::Permission` allowing `s3.amazonaws.com` to invoke, scoped via a hardcoded `SourceArn` to break the classic bucket↔notification circular dep - `AWS::S3::Bucket` `pipeline-source` with `s3:ObjectCreated:*` notification to the Lambda, `DependsOn` the permission Verified: uploading `test/obj-1776798468.txt` produced a matching DynamoDB item with `bucket=pipeline-source`, `size=20`, `event_time=2026-04-21T19:07:49.155Z`.

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/XkzGvD8XB9BdzY3M_sg3M/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 PASSED      [100%]

=============================== warnings summary ===============================
test_state.py: 21 warnings
  /root/.cache/uv/archive-v0/XkzGvD8XB9BdzY3M_sg3M/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
PASSED ../tests/test_state.py::test_end_to_end_put_creates_ddb_item
======================= 13 passed, 21 warnings in 2.43s ========================

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_ed3f8dc7b1bb42bc. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_ed3f8dc7b1bb42bc · verifier authoritative; classifier explanatory.