zulip/docs/development/setup/vscode-vagrant.md

If your preferred editor is Visual Studio Code, the Visual Studio Code Remote - SSH extension is recommended for editing files when developing with Vagrant. When you have it installed, you can run:

$ code .

to open VS Code connected to your Vagrant environment. See the [Remote development over SSH][remote-ssh] tutorial for more information.

When using this plugin with Vagrant, you will want to run the command vagrant ssh-config from your zulip folder:

$ vagrant ssh-config
Host default
  HostName 127.0.0.1
  User vagrant
  Port 2222
  UserKnownHostsFile /dev/null
  StrictHostKeyChecking no
  PasswordAuthentication no
  IdentityFile /PATH/TO/zulip/.vagrant/machines/default/docker/private_key
  IdentitiesOnly yes
  LogLevel FATAL
  PubkeyAcceptedKeyTypes +ssh-rsa
  HostKeyAlgorithms +ssh-rsa

Then copy that config into your ~/.ssh/config file. You may want to change the host name from default to something more descriptive, like zulip. Finally, refresh the known remotes in Visual Studio Code's Remote Explorer.