fix(cdk): unstable CloudFront function name

- The bug that a CloudFront function name fluctuated over deployment to
  deployment is worked around. There is a bug in CDK that it may
  generate different function names at different deployments. Please see
  the following issue for more details,
    - aws/aws-cdk#15523

  As suggested in the above issue, I decided to give a fixed name to my
  CloudFront function. Function names never conflict between development
  and production stacks because `Node.addr` that is different between
  them is appended.

issue codemonger-io#2

cdk/lib/contents-distribution.ts

@@ -5,7 +5,7 @@ import {
   aws_cloudfront as cloudfront,
   aws_cloudfront_origins as origins,
 } from 'aws-cdk-lib';
-import { Construct } from 'constructs';
+import { Construct, Node } from 'constructs';
 
 import { ContentsBucket } from './contents-bucket';
 import { DeploymentStage } from './deployment-stage';
@@ -48,6 +48,14 @@ export class ContentsDistribution extends Construct {
     });
 
     const expandIndexFn = new cloudfront.Function(this, 'ExpandIndexFunction', {
+      // provides a fixed function name because there is a bug in CDK that may
+      // generate different function IDs at different deployments and ends up
+      // with an error updating a function.
+      // see https://github.com/aws/aws-cdk/issues/15523
+      //
+      // note that a function name must be at most 64 characters long,
+      // and Node.addr fills 42 characters.
+      functionName: `ExpandIndexFunction${Node.of(this).addr}`,
       comment: 'Expands a given URI so that it ends with index.html',
       code: cloudfront.FunctionCode.fromFile({
         filePath: path.resolve('cloudfront-fn', 'expand-index.js'),
@@ -68,7 +76,8 @@ export class ContentsDistribution extends Construct {
           }],
           // only static contents are served so far
           cachedMethods: cloudfront.CachedMethods.CACHE_GET_HEAD,
-          viewerProtocolPolicy: cloudfront.ViewerProtocolPolicy.REDIRECT_TO_HTTPS,
+          viewerProtocolPolicy:
+            cloudfront.ViewerProtocolPolicy.REDIRECT_TO_HTTPS,
         },
         // do not add a slash (/) before the root object name.
         defaultRootObject: 'index.html',