feat: do not wait for AWS emulator to start

Author: ceecko

README.md

@@ -50,8 +50,10 @@ It also adds an environment variable for each created state machine that contain
 - `lambdaEndpoint` (defaults to `http://localhost:4000`) the endpoint for the lambda service
 - `path` (defaults to `./.step-functions-local`) the path to store the downloaded step function executables
 - `TaskResourceMapping` allows for Resource ARNs to be configured differently for local development
-- `startStepFunctionsLocalApp` (default: true) starts AWS step function emulator. Set to false if it's running already. It needs to run on port 8083.  
-
+- `startStepFunctionsLocalApp` (default: `true`) starts AWS step function emulator. Set to false if it's running already. It needs to run on port 8083.  
+- `waitToStart` (default: `true`) waits on startup until AWS step function emulator is detected on port 8083
+  - `true` throws an error and stops serverless if emulator is not detected
+  - `false` emits an error to console and keeps serverless running if emulator is not detected
 
 ### Full Config Example
 
@@ -76,6 +78,7 @@ custom:
       FirstState: arn:aws:lambda:us-east-1:101010101010:function:hello
       FinalState: arn:aws:lambda:us-east-1:101010101010:function:hello
     startStepFunctionsLocalApp: true
+    waitToStart: true
 
 functions:
   hello:

index.js

@@ -34,6 +34,10 @@ class ServerlessStepFunctionsLocal {
       this.config.startStepFunctionsLocalApp = true
     }
 
+    if (this.config.waitToStart === undefined) {
+      this.config.waitToStart = true
+    }
+
     this.stepfunctionsServer = new StepFunctionsLocal(this.config);
 
     this.stepfunctionsAPI = new AWS.StepFunctions({endpoint: 'http://localhost:8083', region: this.config.region});
@@ -44,9 +48,19 @@ class ServerlessStepFunctionsLocal {
           await this.installStepFunctions();
         }
 
-        await this.startStepFunctions();
-        await this.getStepFunctionsFromConfig();
-        await this.createEndpoints();
+        const bootstrap = (async () => {
+          await this.startStepFunctions();
+          await this.getStepFunctionsFromConfig();
+          await this.createEndpoints();
+        })()
+
+        if(this.config.waitToStart) {
+          await bootstrap;
+        } else {
+          bootstrap.catch(err => {
+            console.error(chalk.red('[Serverless Step Functions Local]'), 'Could not detect AWS Step Functions emulator running on port 8083.');
+          })
+        }
       },
       'before:offline:start:end': async () => {
         if (this.config.startStepFunctionsLocalApp) {