Summary

Using optimism-integration to create a custom network on MetaMask does not work as expected (as explained in the developer docs).

Explanation of issue

In the developer docs, there is a section with steps to setup the optimism-integration repo. Here's a snapshot of the section I'm referring to:

Once the containers are running, I tried to connect to either localhost:9545 or localhost:8545, which the docs imply are available to connect. In MetaMask, I try creating a new custom network with the RPC url as http://localhost:9545 and the chainID as 420, but I receive this error instead:

Steps to Reproduce

1. Follow the steps under the "[Using the optimism-integration Repo]"(http://community.optimism.io/docs/developers/integration.html#using-the-optimism-integration-repo) to spin up the complete L1/L2 dev environment, and leave the containers running
2. Try to create a new custom network in MetaMask, using http://localhost:9545 as the "New RPC URL" and 420 as the "Chain ID".
3. Click "Save"
4. See the error shown above.

Additional notes

After chatting with @maurelian, he suggested I use http://0.0.0.0:9545, however, when doing so, I get this more helpful error:

Using that chainID, 31337 lets MetaMask create the custom network, no problem.

@kfichter Wondering if I'm doing something wrong or if there's something missing from the docs?