fix(docker): make LocalStack container lookup explicitly configurable (#14)

Author: HarshCasper

README.md

@@ -94,6 +94,13 @@ Here's how to add your LocalStack Auth Token to the environment variables:
 }
 ```
 
+## LocalStack Configuration
+
+| Variable Name | Description | Default Value |
+| ------------- | ----------- | ------------- |
+| `LOCALSTACK_AUTH_TOKEN` | The LocalStack Auth Token to use for the MCP server | None |
+| `MAIN_CONTAINER_NAME` | The name of the LocalStack container to use for the MCP server | `localstack-main` |
+
 ## Contributing
 
 Pull requests are welcomed on GitHub! To get started:

src/lib/docker/docker.client.test.ts

@@ -57,6 +57,8 @@ describe("DockerApiClient", () => {
     mocks.getContainer.mockImplementation(() => ({ exec: mocks.exec }));
     mocks.exec.mockImplementation(async () => ({ start: mocks.start, inspect: mocks.execInspect }));
     mocks.__state.demuxTarget = "stdout";
+    delete process.env.MAIN_CONTAINER_NAME;
+    delete process.env.LOCALSTACK_MAIN_CONTAINER_NAME;
   });
 
   test("findLocalStackContainer throws when none found", async () => {
@@ -77,6 +79,29 @@ describe("DockerApiClient", () => {
     await expect(client.findLocalStackContainer()).resolves.toBe("abc123");
   });
 
+  test("findLocalStackContainer matches MAIN_CONTAINER_NAME when configured", async () => {
+    process.env.MAIN_CONTAINER_NAME = "my-custom-localstack";
+
+    const mocks = getDockerMocks();
+    mocks.listContainers.mockResolvedValueOnce([
+      { Id: "not-this", Names: ["/localstack-main"] },
+      { Id: "xyz999", Names: ["/my-custom-localstack"] },
+    ]);
+
+    const client = new DockerApiClient();
+    await expect(client.findLocalStackContainer()).resolves.toBe("xyz999");
+  });
+
+  test("findLocalStackContainer throws when only compose-prefixed name exists without config", async () => {
+    const mocks = getDockerMocks();
+    mocks.listContainers.mockResolvedValueOnce([{ Id: "compose123", Names: ["/project-localstack-1"] }]);
+
+    const client = new DockerApiClient();
+    await expect(client.findLocalStackContainer()).rejects.toThrow(
+      /Could not find a running LocalStack container named "localstack-main"/i
+    );
+  });
+
   test("executeInContainer returns stdout on success", async () => {
     const mocks = getDockerMocks();
     mocks.listContainers.mockResolvedValueOnce([{ Id: "abc123", Names: ["/localstack-main"] }]);

src/lib/docker/docker.client.ts

@@ -14,21 +14,43 @@ export class DockerApiClient {
     this.docker = new DockerCtor();
   }
 
+  private normalizeContainerName(name?: string): string {
+    if (!name) return "";
+    return name.startsWith("/") ? name.slice(1) : name;
+  }
+
+  private matchesConfiguredContainerName(
+    container: { Names?: string[] },
+    configuredName: string
+  ): boolean {
+    return (container.Names || []).some(
+      (n) => this.normalizeContainerName(n) === configuredName
+    );
+  }
+
   async findLocalStackContainer(): Promise<string> {
     const running = (await (this.docker.listContainers as any)({
       filters: { status: ["running"] },
-    })) as Array<{ Id: string; Names?: string[] }>;
-
-    const match = (running || []).find((c) =>
-      (c.Names || []).some((n) => {
-        const name = (n || "").startsWith("/") ? n.slice(1) : n;
-        return name === "localstack-main";
-      })
+    })) as Array<{
+      Id: string;
+      Names?: string[];
+    }>;
+
+    const configuredName = (
+      process.env.MAIN_CONTAINER_NAME ||
+      process.env.LOCALSTACK_MAIN_CONTAINER_NAME ||
+      "localstack-main"
+    ).trim();
+
+    const byConfiguredName = (running || []).find((c) =>
+      this.matchesConfiguredContainerName(c, configuredName)
     );
+    if (byConfiguredName) return byConfiguredName.Id as string;
 
-    if (match) return match.Id as string;
-
-    throw new Error("Could not find a running LocalStack container named 'localstack-main'.");
+    throw new Error(
+      `Could not find a running LocalStack container named "${configuredName}". ` +
+        `Set MAIN_CONTAINER_NAME to your container name if it is custom.`
+    );
   }
 
   async executeInContainer(