Allow specifying a retention policy for lambda layers

docs/providers/aws/guide/layers.md

@@ -36,6 +36,7 @@ layers:
     licenseInfo: GPLv3 # optional, a string specifying license information
     allowedAccounts: # optional, a list of AWS account IDs allowed to access this layer.
       - '*'
+    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.

docs/providers/aws/guide/serverless.yml.md

@@ -262,6 +262,18 @@ functions:
           pool: MyUserPool
           trigger: PreSignUp
 
+layers:
+  hello: # A Lambda layer
+    path: layer-dir # required, path to layer contents on disk
+    name: ${self:provider.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
+      - python3.7
+    licenseInfo: GPLv3 # optional, a string specifying license information
+    allowedAccounts: # optional, a list of AWS account IDs allowed to access this layer.
+      - '*'
+    retain: false # optional, false by default. If true, layer versions are not deleted as new ones are created
+
 # The "Resources" your "Functions" use.  Raw AWS CloudFormation goes in here.
 resources:
   Resources:

lib/plugins/aws/package/compile/layers/index.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const crypto = require('crypto');
 const BbPromise = require('bluebird');
 const _ = require('lodash');
 const path = require('path');
@@ -49,7 +50,12 @@ class AwsCompileLayers {
       newLayer.Properties.CompatibleRuntimes = layerObject.compatibleRuntimes;
     }
 
-    const layerLogicalId = this.provider.naming.getLambdaLayerLogicalId(layerName);
+    let layerLogicalId = this.provider.naming.getLambdaLayerLogicalId(layerName);
+    if (layerObject.retain) {
+      const sha = crypto.createHash('sha1').update(JSON.stringify(newLayer)).digest('hex');
+      layerLogicalId = `${layerLogicalId}${sha}`;
+      newLayer.DeletionPolicy = 'Retain';
+    }
     const newLayerObject = {
       [layerLogicalId]: newLayer,
     };

lib/plugins/aws/package/compile/layers/index.test.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const crypto = require('crypto');
 const path = require('path');
 const chai = require('chai');
 const AwsProvider = require('../../../provider/awsProvider');
@@ -118,6 +119,48 @@ describe('AwsCompileLayers', () => {
       });
     });
 
+    it('should create a layer resource with a retention policy', () => {
+      const s3Folder = awsCompileLayers.serverless.service.package.artifactDirectoryName;
+      const s3FileName = awsCompileLayers.serverless.service.layers.test.package.artifact
+        .split(path.sep).pop();
+      awsCompileLayers.serverless.service.layers = {
+        test: {
+          path: 'layer',
+          retain: true,
+        },
+      };
+      const compiledLayer = {
+        Type: 'AWS::Lambda::LayerVersion',
+        Properties: {
+          Content: {
+            S3Bucket: { Ref: 'ServerlessDeploymentBucket' },
+            S3Key: `${s3Folder}/${s3FileName}`,
+          },
+          LayerName: 'test',
+        },
+      };
+      const sha = crypto.createHash('sha1').update(JSON.stringify(compiledLayer)).digest('hex');
+      compiledLayer.DeletionPolicy = 'Retain';
+      const compiledLayerOutput = {
+        Description: 'Current Lambda layer version',
+        Value: {
+          Ref: `TestLambdaLayer${sha}`,
+        },
+      };
+
+      return expect(awsCompileLayers.compileLayers()).to.be.fulfilled
+      .then(() => {
+        expect(
+          awsCompileLayers.serverless.service.provider.compiledCloudFormationTemplate
+          .Resources[`TestLambdaLayer${sha}`]
+        ).to.deep.equal(compiledLayer);
+        expect(
+          awsCompileLayers.serverless.service.provider.compiledCloudFormationTemplate
+            .Outputs.TestLambdaLayerQualifiedArn
+        ).to.deep.equal(compiledLayerOutput);
+      });
+    });
+
     it('should create a layer resource with permissions', () => {
       const s3Folder = awsCompileLayers.serverless.service.package.artifactDirectoryName;
       const s3FileName = awsCompileLayers.serverless.service.layers.test.package.artifact