Serverless Aws Alias

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Serverless AWS alias plugin

The plugin requires Serverless 1.12 or later!

This plugin enables use of AWS aliases on Lambda functions. The term alias must not be mistaken as the stage. Aliases can be deployed to stages, e.g. if you work on different VCS branches in the same service, you can deploy your branch to a new alias. The alias deployment can contain a different set of functions (newly added ones or removed ones) and does not impact any other deployed alias. Aliases also can be used to provide a ‘real’ version promotion.

As soon as the service is deployed with the plugin activated, it will create a default alias that is named equally to the stage. This is the master alias for the stage.

Each alias creates a CloudFormation stack that is dependent on the stage stack. This approach has multiple advantages including easy removal of any alias deployment, protecting the aliased function versions, and many more.

Installation

Add the plugin to your package.json’s devDependencies and to the plugins array in your serverless.yml file. After installation the plugin will automatically hook into the deployment process. Additionally the new alias command is added to Serverless which offers some functionality for aliases.

Deploy the default alias

The default alias (for the stage) is deployed just by doing a standard stage deployment with serverless deploy. From now on you can reference the aliased versions on Lambda invokes with the stage qualifier. The aliased version is read only in the AWS console, so it is guaranteed that the environment and function parameters (memory, etc.) cannot be changed for a deployed version by accident, as it can be done with the $LATEST qualifier. This adds an additional level of stability to your deployment process.

Deploy a single function

The plugin supports serverless deploy function and moves the alias to the updated function version. However you must specify the --force switch on the commandline to enforce Serverless to deploy a new function ZIP regardless, if the code has changed or not. This is necessary to prevent setting the alias to a version of the function that has been deployed by another developer.

Deploy an alias

To deploy an alias to a stage, just add the --alias option to serverless deploy with the alias name as option value.

Example: serverless deploy --alias myAlias

Remove an alias

See the alias remove command below.

Remove a service

To remove a complete service, all deployed user aliases have to be removed first, using the alias remove command.

To finally remove the whole service (same outcome as serverless remove), you have to remove the master (stage) alias with serverless alias remove --alias=MY_STAGE_NAME.

This will trigger a removal of the master alias CF stack followed by a removal of the service stack. After the stacks have been removed, there should be no remains of the service.

The plugin will print reasonable error messages if you miss something so that you’re guided through the removal.

Aliases and API Gateway

In Serverless stages are, as above mentioned, parallel stacks with parallel resources. Mapping the API Gateway resources to this semantics, each stage has its own API deployment.

Aliases fit into this very well and exactly as with functions an alias is a kind of “tag” within the API deployment of one stage. Curiously AWS named this “stage” in API Gateway, so it is not to be confused with Serverless stages.

Thus an alias deployment will create an API Gateway stage with the alias name as name.

API Gateway stage and deployment

The created API Gateway stage has the stage variables SERVERLESS_STAGE and SERVERLESS_ALIAS set to the corresponding values.

If you want to test your APIG endpoints in the AWS ApiGateway console, you have to set the SERVERLESS_ALIAS stage variable to the alias that will be used for the Lambda invocation. This will call the aliased function version.

Deployed stages have the alias stage variable set fixed, so a deployed alias stage is hard-wired to the aliased Lambda versions.

Stage configuration (NEW)

The alias plugin supports configuring the deployed API Gateway stages, exactly as you can do it within the AWS APIG console, e.g. you can configure logging (with or without data/request tracing), setup caching or throttling on your endpoints.

The configuration can be done on a service wide level, function level or method level by adding an aliasStage object either to provider, any function or a http event within a function in your serverless.yml. The configuration is applied hierarchically, where the inner configurations overwrite the outer ones.

HTTP Event -> FUNCTION -> SERVICE

API logs

The generated API logs (in case you enable logging with the loggingLevel property) can be shown the same way as the function logs. The plugin adds the serverless logs api command which will show the logs for the service’s API. To show logs for a specific deployed alias you can combine it with the --alias option as usual.

The aliasStage configuration object

All settings are optional, and if not specified will be set to the AWS stage defaults.

aliasStage:
  cacheDataEncrypted: (Boolean)
  cacheTtlInSeconds: (Integer)
  cachingEnabled: (Boolean)
  dataTraceEnabled: (Boolean) - Log full request/response bodies
  loggingLevel: ("OFF", "INFO" or "ERROR")
  metricsEnabled: (Boolean) - Enable detailed CW metrics
  throttlingBurstLimit: (Integer)
  throttlingRateLimit: (Number)

There are two further options that can only be specified on a service level and that affect the whole stage:

aliasStage:
  cacheClusterEnabled: (Boolean)
  cacheClusterSize: (Integer)

For more information see the AWS::APIGateway::Stage or MethodSettings documentation on the AWS website.

Sample serverless.yml (partial):

service: sls-test-project

provider:
  ...
  # Enable detailed error logging on all endpoints
  aliasStage:
    loggingLevel: "ERROR"
    dataTraceEnabled: true
  ...

functions:
  myFunc1:
    ...
    # myFunc1 should generally not log anything
    aliasStage:
      loggingLevel: "OFF"
      dataTraceEnabled: false
    events:
      - http:
          method: GET
          path: /func1
      - http:
          method: POST
          path: /func1/create
      - http:
          method: PATCH
          path: /func1/update
          # The update endpoint needs special settings
          aliasStage:
            loggingLevel: "INFO"
            dataTraceEnabled: true
            throttlingBurstLimit: 200
            throttlingRateLimit: 100

  myFunc2:
    ...
    # Will inherit the global settings if nothing is set on function level

Reference the current alias in your service

You can reference the currently deployed alias with ${self:provider.alias} in your service YAML file. It should only be used for information, but not to set any resource names. Making anything hard-wired to the alias name might make the project unusable when deployed to different aliases because the resources are maintained in the master CF stack - the plugin takes care that resources are available.

A valid use is to forward the alias name as environment variable to the lambdas and use it there for tagging of log messages. Then you see immediately which aliased lambda is the origin.

Any other use with the further exception of lambda event subscriptions (see below) is strongly discouraged.

Resources

Resources are deployed per alias. So you can create new resources without destroying the main alias for the stage. If you remove an alias the referenced resources will be removed too.

However, logical resource ids are unique per stage. If you deploy a resource into one alias, it cannot be deployed with the same logical resource id and a different configuration into a different alias. Nevertheless, you can have the same resource defined within multiple aliases with the same configuration.

This behavior exactly resembles the workflow of multiple developers working on different VCS branches.

The master alias for the stage has a slightly different behavior. If you deploy here, you are allowed to change the configuration of the resource (e.g. the capacities of a DynamoDB table). This deployment will reconfigure the resource and on the next alias deployment of other developers, they will get an error that they have to update their configuration too - most likely, they updated it already, because normally you rebase or merge your upstream and get the changes automatically.

Event subscriptions

Event subscriptions that are defined for a lambda function will be deployed per alias, i.e. the event will trigger the correct deployed aliased function.

SNS

Subscriptions to SNS topics can be implicitly defined by adding an sns event to any existing lambda function definition. Serverless will create the topic for you and add a subscription to the deployed function.

With the alias plugin the subscription will be per alias. Additionally the created topic is renamed and the alias name is added (e.g. myTopic-myAlias). This is done because SNS topics are independent per stage. Imagine you want to introduce a new topic or change the data/payload format of an existing one. Just attaching different aliases to one central topic would eventually break the system, as functions from different stages will receive the new data format. The topic-per-alias approach effectively solves the problem.

If you want to refer to the topic programmatically, you just can add -${process.env.SERVERLESS_ALIAS} to the base topic name.

Use with global resources

Event subscriptions can reference resources that are available throughout all aliases if they reference the same resource id. That means that an event will trigger all aliases that are deployed with the subscription defined.

Example:

functions:
  testfct1:
    description: 'My test function'
    handler: handlers/testfct1/handler.handle
    events:
      - stream:
          type: kinesis
          arn: "arn:aws:kinesis:${self:provider.region}:XXXXXX:stream/my-kinesis"
      - http:
          method: GET
          path: /func1
resources:
  Resources:
    myKinesis:
      Type: AWS::Kinesis::Stream
      Properties:
        Name: my-kinesis
        ShardCount: 1

When a function is deployed to an alias it will now also listen to the my-kinesis stream events. This is useful, if you want to test new implementations with an existing resource.

Use with per alias resources

Currently this feature is not available. The Serverless framework does not support variable substitution in property names (see #49). As soon as this has been implemented there, this note will be removed.

There might be cases where you want to test with your private resources first, before you deploy changes to the master alias. Or you just want to create separate resources and event subscriptions per alias.

The solution here is to make the resource id dependent on the alias name, so that the alias effectively owns the resource and the event subscription is bound to it.

Example:

functions:
  testfct1:
    description: 'My test function'
    handler: handlers/testfct1/handler.handle
    events:
      - stream:
          type: kinesis
          arn: "arn:aws:kinesis:${self:provider.region}:XXXXXX:stream/my-kinesis-${self.provider.alias}"
      - http:
          method: GET
          path: /func1
resources:
  Resources:
    myKinesis${self:provider.alias}:
      Type: AWS::Kinesis::Stream
      Properties:
        Name: my-kinesis-${self.provider.alias}
        ShardCount: 1

Named streams

The examples above use named streams. I know that this is not perfect as changes that require replacement are not possible. The reason for the named resources is, that Serverless currently only supports event arns that are strings. The change is already in the pipeline there. Afterwards you just can reference the event arns with CF functions like “Fn::GetAtt” or “Ref”. I will update the examples as soon as it is fixed there and publicly available.

Serverless info integration

The plugin integrates with the Serverless info command. It will extend the information that is printed with the list of deployed aliases.

In verbose mode (serverless info -v) it will additionally print the names of the lambda functions deployed to each stage with the version numbers the alias points to.

Given an alias with --alias=XXXX info will show information for the alias.

Serverless logs integration

The plugin integrates with the Serverless logs command (all standard options will work). Additionally, given an alias with --alias=XXXX, logs will show the logs for the selected alias. Without the alias option it will show the master alias (aka. stage alias).

The generated API logs (in case you enable logging with the stage loggingLevel property) can be shown the same way as the function logs. The plugin adds the serverless logs api command which will show the logs for the service’s API. To show logs for a specific deployed alias you can combine it with the --alias option as usual.

The alias command

Subcommands

alias remove

Removes an alias and all its uniquely referenced functions and function versions. The alias name has to be specified with the --alias option.

Functions and resources owned by removed aliases will be physically removed after the alias stack has been removed.

Compatibility

The alias plugin is compatible with all standard Serverless commands and switches. For example, you can use --noDeploy and the plugin will behave accordingly.

Interoperability

Care has to be taken when using other plugins that modify the CF output too. I will add configuration instructions in this section for these plugin combinations.

serverless-plugin-warmup

The warmup plugin will keep your Lambdas warm and reduce the cold start time effectively. When using the plugin, it must be listed before the alias plugin in the plugin list of serverless.yml. The warmup lambda created by the plugin will be aliased too, so that the warmup plugin can be configured differently per deployed alias.

Test it

In case you wanna test how it behaves, I provided a predefined test service in the sample folder, that creates two functions and a DynamoDB table. Feel free to check everything - and of course report bugs immediately ;-) as I could not test each and every combination of resources, functions, etc.

Use case examples

Multiple developers work on different branches

A common use case is that multiple developers work on different branches on the same service, e.g. they add new functions individually. Every developer can just deploy his version of the service to different aliases and use them. Neither the main (stage) alias is affected by them nor the other developers.

If work is ceased on a branch and it is deleted, the alias can just be removed and on the next deployment of any other alias, the obsoleted functions will disappear automatically.

Sample project

A preconfigured sample project can be found here. It lets you start testing right away. See the project’s README for instructions. The sample project will evolve over time - when new features or changes are integrated into the plugin.

Uninstall

If you are not happy with the plugin or just do not like me, you can easily get rid of the plugin without doing any harm to the deployed stuff. The plugin is non-intrusive and does only add some output variables to the main stack:

You’re all set.

Advanced use cases

VPC settings

Aliases can have different VPC settings (serverless.yml:provider.vpc). So you can use an alias deployment also for testing lambda functions within other internal networks. This is possible because each deployed AWS lambda version contains its entire configuration (VPC settings, environment, etc.)

For developers

Lifecycle events

currently the exposed hooks are not available after the change to the new SLS lifecycle model

The plugin adds the following lifecycle events that can be hooked by other plugins:

CF template information (not yet implemented)

If you hook after the alias:deploy:loadTemplates hook, you have access to the currently deployed CloudFormation templates which are stored within the global Serverless object: serverless.service.provider.deployedCloudFormationTemplate and serverless.service.provider.deployedAliasTemplates[].

Ideas

Version history