Record resolving order in the sequencer and start modules based on that

packages/sequencer/src/sequencer/executor/Sequencer.ts

@@ -66,6 +66,14 @@ export class Sequencer<Modules extends SequencerModulesRecord>
    * modules to start each
    */
   public async start() {
+    // The sequencer uses tsyringe to resolve modules (and their dependencies)
+    // and then starts them. However, this can be problematic as although tsyringe may resolve
+    // dependencies, it doesn't actually start them. For example, a database may be created,
+    // but the connection strings, etc, won't be constructed until it's started, and this may
+    // cause an error if a module that relies on it is started first. The way to fix this is
+    // ensure that we start modules based on the order they were resolved.
+    // We iterate through the methods three times:
+
     this.useDependencyFactory(this.container.resolve(MethodIdFactory));
 
     // Log startup info
@@ -75,15 +83,41 @@ export class Sequencer<Modules extends SequencerModulesRecord>
     log.info("Starting sequencer...");
     log.info("Modules:", moduleClassNames);
 
+    // Iteration #1: We invoke the afterResolution feature for the container
+    // to ensure every time a module is resolved it gets recorded.
+    const orderedModules: Extract<keyof Modules, string>[] = [];
+    // eslint-disable-next-line guard-for-in
+    for (const moduleName in this.definition.modules) {
+      this.container.afterResolution(
+        moduleName,
+        () => {
+          orderedModules.push(moduleName);
+        },
+        {
+          frequency: "Once",
+        }
+      );
+    }
+    // Iteration #2: We resolve each module and thus populate
+    // the orderedModules list to understand the sequencing.
     // eslint-disable-next-line guard-for-in
     for (const moduleName in this.definition.modules) {
       const sequencerModule = this.resolve(moduleName);
-
       log.info(
-        `Starting sequencer module ${moduleName} (${sequencerModule.constructor.name})`
+        `Resolving sequencer module ${moduleName} (${sequencerModule.constructor.name})`
       );
+    }
+
+    // Iteration #3: We now iterate though the orderedModules list
+    // and start the modules in the order they were resolved.
+    for (const moduleName of orderedModules) {
+      const sequencerModule = this.resolve(moduleName);
       // eslint-disable-next-line no-await-in-loop
       await sequencerModule.start();
+
+      log.info(
+        `Starting sequencer module ${moduleName} (${sequencerModule.constructor.name})`
+      );
     }
   }
 }