The Serve CLI and REST API always sets the host to `0.0.0.0` and the port to Serve's default. This change adds `host` and `port` as top level options in the Serve config file, so users can manually set the host and port of their Serve application to different values.
This change introduces a new Serve config file format:
```yaml
import_path: ...
runtime_env: ...
host: ...
port: ...
deployments: ...
...
```
`host` and `port` are optional and can be omitted. A running Serve application's `host` and `port` cannot be changed. If a user tries to `serve deploy` a config file with different `host` and `port` options than an already-running Serve application, `serve deploy` will fail without making any changes to the application. The user must `serve shutdown` their application and restart it with `serve deploy` to change their `host` and `port`.
**Follow-Up Items**
* The following CLI commands should **not** start Serve automatically. They should check whether Serve is running and perform some sort of no-op if it's not. That would alleviate the concern that the user starts Serve by accident through a `GET` request and needs to deal with default `host`/`port` options. Corresponding docs should also be updated.
* `serve status`
* `serve config`
* `serve shutdown`
ray.init() will currently start a new Ray instance even if one is already existing, which is very confusing if you are a new user trying to go from local development to a cluster. This PR changes it so that, when no address is specified, we first try to find an existing Ray cluster that was created through `ray start`. If none is found, we will start a new one.
This makes two changes to the ray.init() resolution order:
1. When `ray start` is called, the started cluster address was already written to a file called `/tmp/ray/ray_current_cluster`. For ray.init() and ray.init(address="auto"), we will first check this local file for an existing cluster address. The file is deleted on `ray stop`. If the file is empty, autodetect any running cluster (legacy behavior) if address="auto", or we will start a new local Ray instance if address=None.
2. When ray.init(address="local") is called, we will create a new local Ray instance, even if one is already existing. This behavior seems to be necessary mainly for `ray.client` use cases.
This also surfaces the logs about which Ray instance we are connecting to. Previously these were hidden because we didn't set up the log until after connecting to Ray. So now Ray will log one of the following messages during ray.init:
```
(Connecting to existing Ray cluster at address: <IP>...)
...connection...
(Started a local Ray cluster.| Connected to Ray Cluster.)( View the dashboard at <URL>)
```
Note that this changes the dashboard URL to be printed with `ray.init()` instead of when the dashboard is first started.
Co-authored-by: Eric Liang <ekhliang@gmail.com>
#25575 starts all Serve actors in the `"serve"` namespace. This change updates the Serve documentation to remove now-outdated explanations about namespaces and to specify that all Serve actors start in the `"serve"` namespace.
