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Debugging
1

Effectively debugging web apps takes effort, especially when an HTTP request goes through multiple layers before reaching your web app. Follow the steps below to debug a specific app.

You can choose to debug in an environment deployed to {{< vendor/name >}} or with your app running locally but connected to deployed services. In either case, make sure to debug in a non-production environment.

{{% troubleshoot %}}

1. Create a new environment

Start by creating a new environment completely isolated from production but with the same data for debugging:

platform branch debug-branch

2. Get access

{{< codetabs >}}

+++ title=Remote +++

Access your app container via SSH:

platform ssh

<--->

+++ title=Local +++

To access deployed apps and services, open tunnels to everything your app has relationships with:

platform tunnel:open

In the same terminal, set the relevant environment variables:

export PLATFORM_RELATIONSHIPS="$(platform tunnel:info --encode)"
export PORT=8888

{{< /codetabs >}}

3. Run your app in inspect mode

{{< codetabs >}}

+++ title=Remote +++

Stop the current process and restart it in inspect mode:

sv stop app
node --inspect <START_FILE>

<--->

+++ title=Local +++

In the same terminal as the previous step, run the following command:

node --inspect <START_FILE>

{{< /codetabs >}}

Replace <START_FILE> with the file defined for your app's start command.

You get output something like this:

Debugger listening on ws://127.0.0.1:9229/10701e5d-d627-4180-a967-d47a924c93c0
For help, see: https://nodejs.org/en/docs/inspector
Listening on port 8888

4. (If debugging remotely) Forward the debugger port locally

In another terminal, create an SSH tunnel that forwards to the 9229 port:

ssh -N -L 9229:localhost:9229 $(platform ssh --pipe)

5. Connect the debugger

You can now connect the debugger as if you were debugging a local application. See examples with some common tools:

{{< codetabs >}}

+++ title=Using Chrome developer tools +++

Go to chrome://inspect. Find your running app under the Remote Target list. Click inspect to start the debugger.

<--->

+++ title=Using Visual Studio Code +++

Use the Node.js: Attach debugger option.

If you haven't created the option:

  1. On the Run and Debug tab, click create a launch.json file.
  2. Select Node.js as the environment.
  3. In the configurations array, start IntelliSense (usually ctrl+space).
  4. Select Node.js: Attach.
  5. Make sure the port is the same as in step 4 above.

Once you have the option:

In the Run and Debug tab, select Attach from the menu and click Start Debugging (the green arrow).

See more on Node.js debugging in Visual Studio Code.

{{< /codetabs >}}

Now when you load the site at your deployed URL (if debugging remote) or localhost (if debugging locally), the local debugger you've attached is called.

Set breakpoints:

{{< codetabs >}}

+++ title=Remote +++

In the JavaScript files from your remote site: On the Run and Debug tab under Loaded Scripts find Attach: Remote Process > /app.

<--->

+++ title=Local +++

Directly in your source files.

{{< /codetabs >}}

Other issues

pm2 process manager blocks other processes

If you're using the pm2 process manager to start your app from a script, you might find it daemonizes itself and blocks other processes (such as backups) by constantly respawning. This may happen even if you use the --no-daemon flag.

Instead of using a script, call pm2 start directly in your start command.