> For the complete documentation index, see [llms.txt](https://anon-coders-notes.gitbook.io/techwriterdev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://anon-coders-notes.gitbook.io/techwriterdev/cloud/aws/developerassociate/services/22_sam/00_basics.md). # Serverless Application Model - SAM ## Mascot ![AWS SAM Mascot](https://574639531-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FJDnjsv52I3fJ56WbLgHu%2Fuploads%2Fgit-blob-c890d2c1c0a08af91975b2543d35dc63c5487ab9%2FSAM_Mascot.png?alt=media) ## About * Transform header indicates it's SAM model. * **Framework for developing and deploying serverless applications**. * All the configuration is `YAML` code. * Generate complex CloudFormation from simple SAM `YAML` file. * Supports anything from CloudFormation such as `Outputs`, `Mappings`, `Parameters`, `Resources` etc. * SAM can use `CodeDeploy` to deploy Lambda functions. * **SAM can help you to run Lambda, API Gateway, DynamoDB locally**. * `samconfig.toml` defines the configuration file for SAM application. Should be at root of the location. * `template.yaml` file which consists of sam template to be deployed at the root of the application. ### SAM Recipe * Transform Header at the top indicates it's SAM template. ```yaml Transform: 'AWS::Serverless-2016-10-31' ``` * Write code using [SAM constructs](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-specification-resources-and-properties.html) * Once SAM template YAML file is created, use `sam deploy` command *( optionally can use `sam package` command)*. * `sam deploy --guided` will enable us to do interactive deployment. * `sam build` transforms sam template to cloud formation template. * Once build completes, artifacts are generated which will be present in folder `aws-sam`. * [SAM commands](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-command-reference.html) helps to build and deploy sam template. * Can use `sam sync --watch` command to quickly sync local changes to AWS Lambda using `SAM Accelerate`. ### Deep Dive 1. SAML Template YAML is first build using `sam build` command. 2. After build phase, cloud formation template *(YAML)* file is generated out of it. 3. Zip and upload S3 the artifacts generated to S3 bucket. 4. Use `sam deploy` command to deploy or execute the changeset. 5. CloudFormation stack is made up of `Lambda`, `API Gateway` and `DynamoDB`. ### SAM Accelerate * It is a set of features to reduce latency while deploying resources to AWS. * `sam sync` synchronizes the project declared in SAM templates to AWS. * It can synchronize code changes to AWS without updating infrastructure *(internally it uses service APIs and bypass CloudFormation)*. #### `sync` command | Command | Description | | --------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------ | | `sam sync` | Synchronizes code and infrastructure | | `sam sync --code` | Synchronizes code changes without updating infrastructure *(bypass CloudFormation, update in seconds)* | | `sam sync --code --resource ` | Synchronize only a specific resource and their dependencies | | `sam sync --code --resource-id ` | Synchronize only resource with specific resource id and their dependencies | | `sam sync --watch` |

Monitor for file changes and automatically synchronize when changes are detected.
If includes configuration changes, it uses sam sync

| ### SAM policy templates * It is a list of templates to apply permission to your Lambda functions. * Policy templates list can be found [here](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-policy-template-list.html). * From the above policy list following are important. * `S3ReadPolicy` * `SQSPollerPolicy` * `DynamoDBCrudPolicy` ### Local Capability #### Lambda **Start Lambda** * By using SAM framework, you can start AWS Lambda locally. * This will start a local endpoint that emulates AWS Lambda. * This can be used to run automated test against local endpoint. * Command : `sam local start-lambda`. **Invoke Lambda** * Local invocation can be done using `sam local invoke` command. * Local invocation will invoke lambda once and quit after invocation completes. * Helpful for generating test cases. * If lambda tries to access some other AWS resource make sure to pass the relevant profile using the `--profile` option. **Generate Event** * Generate events for lambda functions using command `sam local generate-event`. #### API Gateway * Locally start an API Gateway endpoint using the command `sam local start-api`. * Starts a local `HTTP` server that hosts all your functions. * Changes to functions are automatically reloaded. ### Multiple environments * [TOML](https://toml.io/en/) file can be used to configure environment specific parameters. * This configuration file can be passed while deploying resources using `SAM` command line. * Command can be given as follows, ```sh sam deploy --config-env # Example sam deploy --config-env prod ``` ## Integrations ### SAM and CodeDeploy * SAM Framework natively uses CodeDeploy to update and LambdaFunctions. * Traffic Shifting features using Alias is used for update. * `AutoPublishAlias` Parameter in `SAM` template file takes care of this. * Pre and Post traffic hooks feature to validate deployment *(before traffic shift starts and after it ends)*. * Easy and automated rollbacks using `CloudWatch` Alarms. * Also has capability to provide Deployment Preference like `Canary`, `Linear`, `AllAtOnce`. * Alarms can trigger a rollback.