feat: add warmer lambda function (#6)

Author: rehanvdm

.projen/deps.json

@@ -36,7 +36,7 @@ const project = new awscdk.AwsCdkConstructLibrary({
   peerDeps: ['tailscale-lambda-extension'],
   // description: undefined,  /* The description is just a string that helps people understand the purpose of the package. */
   devDeps: ['husky'], /* Build dependencies for this module. */
-  bundledDeps: ['@types/aws-lambda', '@aws-lambda-powertools/metrics', 'socks-proxy-agent'],
+  bundledDeps: ['@types/aws-lambda', '@aws-lambda-powertools/metrics', 'socks-proxy-agent', '@aws-sdk/client-lambda'],
   publishToPypi: {
     distName: 'tailscale_lambda_proxy',
     module: 'tailscale_lambda_proxy',
@@ -56,10 +56,18 @@ project.gitignore.addPatterns('*.DS_Store');
 
 project.bundler.addBundle('./src/lambda/tailscale-proxy/', {
   platform: 'node',
-  target: 'node20',
+  target: 'node22',
   sourcemap: true,
 });
 project.postCompileTask.exec('cp assets/lambda/tailscale-proxy/index.js lib/lambda/tailscale-proxy/index.js');
 project.postCompileTask.exec('cp assets/lambda/tailscale-proxy/index.js lib/lambda/tailscale-proxy/index.js.map');
 
+project.bundler.addBundle('./src/lambda/proxy-warmer/', {
+  platform: 'node',
+  target: 'node22',
+  sourcemap: true,
+});
+project.postCompileTask.exec('cp assets/lambda/proxy-warmer/index.js lib/lambda/proxy-warmer/index.js');
+project.postCompileTask.exec('cp assets/lambda/proxy-warmer/index.js lib/lambda/proxy-warmer/index.js.map');
+
 project.synth();

.projen/tasks.json

@@ -86,6 +86,10 @@ export class MyStack extends cdk.Stack {
       //   }
       // },
       // debug: true, // Enable debug logging, show request + response, search for lines starting with "[tailscale-"
+      // warmer: { // Optional, enables a "warmer" Lambda to keep proxy connections open/warm (cold start is about 5-10 seconds)
+      //   functionName: name("tailscale-proxy-warmer"),
+      //   concurrentInvocations: 2,
+      // }
     });
 
     const caller = new NodejsFunction(this, "tailscale-caller", {
@@ -182,6 +186,16 @@ A Proxy Lambda error can be identified by the following headers in the response:
 - `ts-error-name`: The error name.
 - `ts-error-message`: The error message.
 
+### Reducing Cold starts
+
+Cold starts occur when your function first has to connect to the Tailscale network, which can take between 5-10 seconds
+as mentioned in the [Tailscale Lambda Extension](https://github.com/rehanvdm/tailscale-lambda-extension?tab=readme-ov-file#limitations)
+docs. Subsequent requests are much faster as the connection is reused.
+
+Cold starts can be mitigated by configuring a "warmer" Lambda function that periodically invokes the Proxy Lambda. The 
+number of warm connections is determined by the `concurrentInvocations` property. This setup helps maintain a pool of 
+warm connections to the Tailscale network, reducing latency for subsequent requests.
+
 ### Code Examples
 
 Refer to the [tailscale-lambda-proxy-example](https://github.com/rehanvdm/tailscale-lambda-proxy-example) repository

.projenrc.ts

@@ -4,6 +4,8 @@ npm run default
 npm run bundle
 npm run compile
 cp assets/lambda/tailscale-proxy/index.js lib/lambda/tailscale-proxy/index.js
+cp assets/lambda/proxy-warmer/index.js lib/lambda/proxy-warmer/index.js
+
 
 
 # For this proxy package to be used in the -caller project