`sam build --parameter-overrides` fails to override

Description

sam build --parameter-overrides fails to override SAM template yaml Parameters

Setup

• Ubuntu 18.04.3 x86_64
• Python 3.7.3
• aws-cli/1.16.265 Python/3.6.8 Linux/5.0.0-32-generic botocore/1.13.1
• SAM CLI, version 0.23.0
• empty requirements.txt
• arbitrary app.py
• below parampoof.yaml

parampoof.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: |
  Repo of param override failing to override

Parameters:
  GitTag:
    Description: description field on lambda version
    Type: String
    Default: defaultgittag

Resources:
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: .
      AutoPublishAlias: test
      VersionDescription: !Ref GitTag
      Handler: app.lambda_handler
      Runtime: python3.7
      Timeout: 10

Steps to reproduce

sam build \
    --template ./parampoof.yaml \
    --manifest requirements.txt \
    --parameter-overrides "ParameterKey=GitTag,ParameterValue=aabbccdd"
grep aabbccdd .aws-sam/build/template.yaml

Observed result

First…

Building resource 'MyFunction'
Running PythonPipBuilder:ResolveDependencies
Running PythonPipBuilder:CopySource

Build Succeeded

Built Artifacts  : .aws-sam/build
Built Template   : .aws-sam/build/template.yaml

Commands you can use next
=========================
[*] Invoke Function: sam local invoke
[*] Package: sam package --s3-bucket <yourbucket>

Then…

Nothing. grep finds no value of aabbccdd in the file

Expected result

grep should find the value aabbccdd in the file. Likely in Parameters: section by overriding/replacing the default value defaultgittag. This is needed because the next steps sam package and sam deploy in the workflow depend on this .aws-sam/build/template.yaml transformed output of sam build.

Debug output of sam build

Using SAM Template at **redacted**/parampoof.yaml
Telemetry endpoint configured to be https://aws-serverless-tools-telemetry.us-west-2.amazonaws.com/metrics
'build' command is called
Collected default values for parameters: {'GitTag': 'defaultgittag'}
1 resources found in the template
Found Serverless function with name='MyFunction' and CodeUri='.'
Building resource 'MyFunction'
Loading workflow module 'aws_lambda_builders.workflows'
Registering workflow 'PythonPipBuilder' with capability 'Capability(language='python', dependency_manager='pip', application_framework=None)'
Registering workflow 'NodejsNpmBuilder' with capability 'Capability(language='nodejs', dependency_manager='npm', application_framework=None)'
Registering workflow 'RubyBundlerBuilder' with capability 'Capability(language='ruby', dependency_manager='bundler', application_framework=None)'
Registering workflow 'GoDepBuilder' with capability 'Capability(language='go', dependency_manager='dep', application_framework=None)'
Registering workflow 'GoModulesBuilder' with capability 'Capability(language='go', dependency_manager='modules', application_framework=None)'
Registering workflow 'JavaGradleWorkflow' with capability 'Capability(language='java', dependency_manager='gradle', application_framework=None)'
Registering workflow 'JavaMavenWorkflow' with capability 'Capability(language='java', dependency_manager='maven', application_framework=None)'
Registering workflow 'DotnetCliPackageBuilder' with capability 'Capability(language='dotnet', dependency_manager='cli-package', application_framework=None)'
Found workflow 'PythonPipBuilder' to support capabilities 'Capability(language='python', dependency_manager='pip', application_framework=None)'
Running workflow 'PythonPipBuilder'
Running PythonPipBuilder:ResolveDependencies
calling pip download -r **redacted**/requirements.txt --dest /tmp/tmpk1rvadh4
Full dependency closure: set()
initial compatible: set()
initial incompatible: set()
Downloading missing wheels: set()
compatible wheels after second download pass: set()
Build missing wheels from sdists (C compiling True): set()
compatible after building wheels (no C compiling): set()
Build missing wheels from sdists (C compiling False): set()
compatible after building wheels (C compiling): set()
Final compatible: set()
Final incompatible: set()
Final missing wheels: set()
PythonPipBuilder:ResolveDependencies succeeded
Running PythonPipBuilder:CopySource
PythonPipBuilder:CopySource succeeded

Build Succeeded

Built Artifacts  : .aws-sam/build
Built Template   : .aws-sam/build/template.yaml

Commands you can use next
=========================
[*] Invoke Function: sam local invoke
[*] Package: sam package --s3-bucket <yourbucket>
    
Sending Telemetry: {'metrics': [{'commandRun': {'awsProfileProvided': False, 'debugFlagProvided': True, 'region': '', 'commandName': 'sam build', 'duration': 523, 'exitReason': 'success', 'exitCode': 0, 'requestId': '9f3a7fc1-3397-48a2-afe0-22848b8743b4', 'installationId': 'c648e689-e57c-4a3c-a26f-ca6d1fd13041', 'sessionId': 'd5aced2b-51ec-4288-aab8-a47317da031d', 'executionEnvironment': 'CLI', 'pyversion': '3.7.3', 'samcliVersion': '0.23.0'}}]}
HTTPSConnectionPool(host='aws-serverless-tools-telemetry.us-west-2.amazonaws.com', port=443): Read timed out. (read timeout=0.1)

Workaround

Don’t use sam build --parameter-overrides. Instead use sed to search/replace the base template.yaml for a known value to replace/override.

Related

https://github.com/awslabs/aws-sam-cli/issues/572

[rpstreef]

This feature is extremely confusing, my expectations were that sam build is using the parameter overrides flag to create an output artifact that I can use for execution or deployment purposes.

[sanathkr]

@diablodale You have a really good point. sam build should capture the flags provided earlier and pass it along to the next commands. Your mental model makes sense and in fact is more powerful IMO.

I think #1503 is going to enable this capability. Please take a look at the design and provide comments. You have an interesting perspective and I think we can all benefit from it.

Closing this Issue because sam is working as expected