Detail how to use Sceptre hooks to deploy lambda (#983)

In order to deploy Lambda functions using either the AWS CLI
or SAM CLI we need to generate the packaged version of the
Lambda functions first. This patch details how to add the "package"
command using Sceptre hooks in a way that reuses existing Sceptre
config.yaml file information to populate the command details.

Signed-off-by: Thanh Ha <[email protected]>

Co-authored-by: Khai Do <[email protected]>

docs/_source/docs/faq.rst

@@ -95,6 +95,38 @@ be found in these projects:
 - `Sage-Bionetworks Sceptre lambda github template`_
 - `Versant SAM Sceptre skeleton example`_
 
+Another approach is to use the Sceptre `before_launch` hook to run either the
+SAM or CFN "package" command to generate the packaged version of the template.
+
+CloudFormation Example:
+
+```yaml
+template_path: generated/lambda-packaged.json
+stack_name: cfn-lambda-example
+hooks:
+  before_launch:
+    - !cmd >
+        aws --profile {{ stack_group_config.profile }} cloudformation package
+        --template-file templates/cfn-lambda.yaml
+        --s3-bucket {{ stack_group_config.template_bucket_name }}
+        --output json
+        --output-template-file templates/generated/lambda-packaged.json
+```
+
+SAM Example:
+
+```yaml
+template_path: generated/sam-packaged.yaml
+stack_name: sam-example
+hooks:
+  before_launch:
+    - !cmd >
+        sam package --profile {{ stack_group_config.profile }}
+        --s3-bucket {{ stack_group_config.template_bucket_name }}
+        --template-file templates/sam-app.yaml
+        --output-template-file templates/generated/sam-packaged.yaml
+```
+
 .. _SAM CLI: https://github.com/aws/aws-sam-cli
 .. _Sage-Bionetworks Sceptre lambda github template: https://github.com/Sage-Bionetworks-IT/lambda-template
 .. _Versant SAM Sceptre skeleton example: https://github.com/Versent/sam-sceptre