### [Read this on the main serverless docs site](https://www.serverless.com/framework/docs/providers/aws/guide/layers) # AWS - Layers If you are using AWS as a provider, all _layers_ inside the service are [AWS Lambda layers](https://aws.amazon.com/blogs/aws/new-for-aws-lambda-use-any-programming-language-and-share-common-components/). ## Configuration All of the Lambda layers in your serverless service can be found in `serverless.yml` under the `layers` property. ```yml # serverless.yml service: myService provider: name: aws layers: hello: path: layer-dir # required, path to layer contents on disk name: ${sls:stage}-layerName # optional, Deployed Lambda layer name description: Description of what the lambda layer does # optional, Description to publish to AWS compatibleRuntimes: # optional, a list of runtimes this layer is compatible with - python3.8 licenseInfo: GPLv3 # optional, a string specifying license information # allowedAccounts: # optional, a list of AWS account IDs allowed to access this layer. # - '*' # note: uncommenting this will give all AWS users access to this layer unconditionally. retain: false # optional, false by default. If true, layer versions are not deleted as new ones are created ``` You can add up to 5 layers as you want within this property. ```yml # serverless.yml service: myService provider: name: aws layers: layerOne: path: layerOne description: optional description for your layer layerTwo: path: layerTwo layerThree: path: layerThree ``` Your layers can either inherit their packaging settings from the global `package` property. ```yml # serverless.yml service: myService provider: name: aws package: exclude: - layerSourceTarball.tar.gz layers: layerOne: path: layerOne ``` Or you can specify them at the layer level. ```yml # serverless.yml service: myService provider: name: aws layers: layerOne: path: layerOne package: exclude: - layerSourceTarball.tar.gz ``` Keep in mind that all `include` and `exclude` patterns (even when inherited from the service config) are resolved against the layer's `path` and not the service `path`. You can also specify a prebuilt archive to create your layer. When you do this, you do not need to specify the `path` element of your layer. ```yml # serverless.yml service: myService provider: name: aws layers: layerOne: package: artifact: layerSource.zip ``` ## Permissions You can make your layers usable by other accounts by setting the `allowedAccounts` property: ```yml # serverless.yml service: myService provider: name: aws layers: layerOne: path: layerOne allowedAccounts: - 111111111111 # a specific account ID - 222222222222 # a different specific account ID ``` Another example, making the layer publicly accessible: ```yml # serverless.yml service: myService provider: name: aws layers: layerOne: path: layerOne allowedAccounts: - '*' # ALL accounts! ``` ## Using your layers Using the `layers` configuration key in a function makes it possible for your layer with a function ```yml functions: hello: handler: handler.hello layers: - arn:aws:lambda:region:XXXXXX:layer:LayerName:Y ``` To use a layer with a function in the same service, use a CloudFormation Ref. The name of your layer in the CloudFormation template will be your layer name [TitleCased](https://en.wikipedia.org/wiki/Letter_case#Title_Case) (without spaces) and have `LambdaLayer` appended to the end. EG: ```yml layers: test: path: layer functions: hello: handler: handler.hello layers: - { Ref: TestLambdaLayer } ``` You can also configure layers at the service level. EG: ```yml # serverless.yml service: myService provider: name: aws runtime: python3.8 layers: - arn:aws:lambda:us-east-1:xxxxxxxxxxxxx:layer:xxxxx:mylayer1 - arn:aws:lambda:us-east-1:xxxxxxxxxxxxx:layer:xxxxx:mylayer2 functions: hello1: handler: handler.hello1 hello2: handler: handler.hello2 ```