Slack BoltJS on GCP Cloud Run doesn't trigger app.message

Question

Summary

I have a very simple BoltJS app deployed to a very simple GCP Cloud Run service, but I can't Slack to trigger the BoltJS app via sending a message to a Slack channel.

Setup

Below is my setup.

Code

Index.ts (bolt)

import { App } from "@slack/bolt";
import { config } from "dotenv";

// config dotenv
config();

const app = new App({
    token: process.env.SLACK_BOT_TOKEN,
    signingSecret: process.env.SLACK_SIGNING_SECRET
});

// listen to all messages
app.message(/.+/, async ({ message, say }) => {
    console.log(`message: ${JSON.stringify(message)}`);
});

// Start your app
(async () => {
    await app.start(process.env.PORT || 3000);

    console.log("⚡️ Bolt app is running!");
})();

GCP Cloud Run

I deploy my app to Cloud Run with a very standard Dockerfile.

Slack Config

1. The signing secret from Basic Information is configured in GCP correctly
2. The Bot User Auth Token from Install App is configured in GCP correctly
3. The App is installed to the Workspace
4. Enable Events is switched ON in Event Subscriptions
5. The Request URL is configured as https://<my-cloud-run-url>/slack/events
6. Subscribe to bot events includes message.channels
7. ALL Bot Token Scopes have been added

Results

When I deploy a new version of my app to Cloud Run, the deployment completes successfully.

In the LOGS for the Cloud Run service, I see the following, which is triggered by the iife that starts my app in index.ts:

⚡️ Bolt app is running!

MAIN PROBLEM

If I type something in a public channel and hit Enter, I check the logs again, but nothing shows up.

I expect to see a log that shows the message that was just sent, but instead I see no logs.

Answer 1

Summary

We were only able to get messages sent directly to the bot because we only subscribed to bot events. Subscribing to message.channels in the section Subscribe to events on behalf of users worked.

Details

On the Event Subscriptions tab in app config, there are three sections at the bottom:

1. Subscribe to bot events
2. Subscribe to events on behalf of users
3. App unfurl domains

We subscribed to message.channels in #1, not #2.

Why did we choose #1?

Well, the description states: Apps can subscribe to receive events the bot user has access to (like new messages in a channel).

"new messages in a channel"... we were posting in a channel, but nothing happened. Apparently the bot user doesn't have access to new messages in public channels.

Documentation could be improved.