Delay reading config until package:initialize hook

This lets serverless variables be resolved before the config.layerConfig object is parsed.
This fixes #3.

LayerManagerPlugin.js

@@ -44,17 +44,23 @@ function getConfig(serverless) {
 class LayerManagerPlugin {
   constructor(sls, options = {}) {
     this.level = options.v || options.verbose ? 'verbose' : LOG_LEVEL;
-    this.config = getConfig(sls);
 
     info(this, `Invoking layer-manager plugin`);
-    verbose(this, `Config: `, this.config);
 
     this.hooks = {
-      'package:initialize': () => this.installLayers(sls),
+      'package:initialize': () => {
+        this.init(sls);
+        this.installLayers(sls)
+      },
       'before:deploy:deploy': () => this.transformLayerResources(sls)
     };
   }
 
+  init(sls) {
+    this.config = getConfig(sls);
+    verbose(this, `Config: `, this.config);
+  }
+
   installLayer(path) {
     const nodeLayerPath = `${path}/nodejs`;
 
@@ -141,4 +147,4 @@ class LayerManagerPlugin {
   }
 }
 
-module.exports = LayerManagerPlugin;
+module.exports = LayerManagerPlugin;

examples/example-layer-service/serverless.yml

@@ -20,10 +20,11 @@ functions:
       # Note the reference being the TitleCase representation of the layer id followed by "LambdaLayer"
       - {Ref: MyLibLambdaLayer}
 
-#custom:
-#  layerConfig:
-#    installLayers: <boolean>
-#    exportLayers: <boolean>
-#    upgradeLayerReferences: <boolean>
-#    exportPrefix: <prefix used for the names of the exported layers>
+custom:
+  foo: FOO
+  layerConfig:
+    installLayers: true
+    exportLayers: true
+    upgradeLayerReferences: true
+    exportPrefix:  ${self:service}-${self:custom.foo}- # prefix used for the names of the exported layers