# Dependencies - `Depends()` and `Security()`

## `Depends()`

Dependencies are handled mainly with the special function `Depends()` that takes a callable.

Here is the reference for it and its parameters.

You can import it directly from `fastapi`:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

In most cases, the same tool that is used to **run the program on startup** is also used to handle automatic **restarts**.

For example, this could be handled by:

* Docker
* Kubernetes
* Docker Compose
* Docker in Swarm Mode
* Systemd
* Supervisor
* Handled internally by a cloud provider as part of their services
* Others...

## Replication - Processes and Memory

        is KtFirPsiJavaClassSymbol -> firSymbol.fir
        is KtFirAnonymousObjectSymbol -> firSymbol.fir
        else -> error(
            "`${this::class.qualifiedName}` needs to be specially handled by the scope provider or is an unknown" +
                    " ${KtSymbolWithDeclarations::class.simpleName} implementation."
        )
    }

    override fun getMemberScope(classSymbol: KtSymbolWithMembers): KtScope {

        with:
          token: ${{ secrets.FASTAPI_ISSUE_MANAGER }}
          config: >
            {
              "answered": {
                "delay": 864000,
                "message": "Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs."
              },
              "changes-requested": {
                "delay": 2628000,

                request.addArtifact(pomArtifact);
            } else if (metadata instanceof SnapshotArtifactRepositoryMetadata
                    || metadata instanceof ArtifactRepositoryMetadata) {
                // eaten, handled by repo system
            } else {
                request.addMetadata(new MetadataBridge(metadata));
            }
        }

        try {
            repoSystem.install(session, request);

        //    }
        //}
        //try {
        //    return CDef.DefMeta.valueOf(searchName);
        //} catch (IllegalArgumentException ignored) { // not found
        //    return null; // handled later
        //}
    }

    @Override
    public OptionalThing<String> determineAlias(final Locale locale) {
        return OptionalObject.empty();
    }

![SDS decision flow](docs/sds-flow.svg)

### Default CA Flow through istio-agent

![CA Flow](docs/ca.svg)

A single SDS request from Envoy goes through a few different layers in istio-agent.

1. First, the request is handled by the SDS server. This is mostly just an intermediate translation layer exposing
   the `SecretManager` to Envoy, without much business logic. For each resource requested by Envoy, the SDS server

There you can set:

* The "Item ID", used in the path.
* The "Token" used as a query parameter.

!!! tip
    Notice that the query `token` will be handled by a dependency.

With that you can connect the WebSocket and then send and receive messages:

<img src="/img/tutorial/websockets/image05.png">

## Handling disconnections and multiple clients

 * <p>
 * A note to the reader;
 * </p>
 * <p>
 * There are several issues/discussions regarding how "aggregator" plugins should be handled.
 * Read for instance http://docs.codehaus.org/display/MAVEN/Deterministic+Lifecycle+Planning
 * </p>
 * <p>
 * In their current implementation they are "bolted" onto the lifecycle by separating them

The same way, you can define logic (code) that should be executed when the application is **shutting down**. In this case, this code will be executed **once**, **after** having handled possibly **many requests**.