proxy: subzero integration in auth-broker (embedded data-api) (#12474)

## Problem
We want to have the data-api served by the proxy directly instead of
relying on a 3rd party to run a deployment for each project/endpoint.

## Summary of changes
With the changes below, the proxy (auth-broker) becomes also a
"rest-broker", that can be thought of as a "Multi-tenant" data-api which
provides an automated REST api for all the databases in the region.

The core of the implementation (that leverages the subzero library) is
in proxy/src/serverless/rest.rs and this is the only place that has "new
logic".

---------

Co-authored-by: Ruslan Talpa <ruslan.talpa@databricks.com>
Co-authored-by: Alexander Bayandin <alexander@neon.tech>
Co-authored-by: Conrad Ludgate <conrad@neon.tech>

proxy/src/binary/proxy.rs

@@ -31,6 +31,8 @@ use crate::auth::backend::local::LocalBackend;
 use crate::auth::backend::{ConsoleRedirectBackend, MaybeOwned};
 use crate::batch::BatchQueue;
 use crate::cancellation::{CancellationHandler, CancellationProcessor};
+#[cfg(feature = "rest_broker")]
+use crate::config::RestConfig;
 #[cfg(any(test, feature = "testing"))]
 use crate::config::refresh_config_loop;
 use crate::config::{
@@ -47,6 +49,8 @@ use crate::redis::{elasticache, notifications};
 use crate::scram::threadpool::ThreadPool;
 use crate::serverless::GlobalConnPoolOptions;
 use crate::serverless::cancel_set::CancelSet;
+#[cfg(feature = "rest_broker")]
+use crate::serverless::rest::DbSchemaCache;
 use crate::tls::client_config::compute_client_config_with_root_certs;
 #[cfg(any(test, feature = "testing"))]
 use crate::url::ApiUrl;
@@ -246,11 +250,23 @@ struct ProxyCliArgs {
 
     /// if this is not local proxy, this toggles whether we accept Postgres REST requests
     #[clap(long, default_value_t = false, value_parser = clap::builder::BoolishValueParser::new(), action = clap::ArgAction::Set)]
+    #[cfg(feature = "rest_broker")]
     is_rest_broker: bool,
 
     /// cache for `db_schema_cache` introspection (use `size=0` to disable)
     #[clap(long, default_value = "size=1000,ttl=1h")]
+    #[cfg(feature = "rest_broker")]
     db_schema_cache: String,
+
+    /// Maximum size allowed for schema in bytes
+    #[clap(long, default_value_t = 5 * 1024 * 1024)] // 5MB
+    #[cfg(feature = "rest_broker")]
+    max_schema_size: usize,
+
+    /// Hostname prefix to strip from request hostname to get database hostname
+    #[clap(long, default_value = "apirest.")]
+    #[cfg(feature = "rest_broker")]
+    hostname_prefix: String,
 }
 
 #[derive(clap::Args, Clone, Copy, Debug)]
@@ -517,6 +533,17 @@ pub async fn run() -> anyhow::Result<()> {
     ));
     maintenance_tasks.spawn(control_plane::mgmt::task_main(mgmt_listener));
 
+    // add a task to flush the db_schema cache every 10 minutes
+    #[cfg(feature = "rest_broker")]
+    if let Some(db_schema_cache) = &config.rest_config.db_schema_cache {
+        maintenance_tasks.spawn(async move {
+            loop {
+                tokio::time::sleep(Duration::from_secs(600)).await;
+                db_schema_cache.flush();
+            }
+        });
+    }
+
     if let Some(metrics_config) = &config.metric_collection {
         // TODO: Add gc regardles of the metric collection being enabled.
         maintenance_tasks.spawn(usage_metrics::task_main(metrics_config));
@@ -679,6 +706,30 @@ fn build_config(args: &ProxyCliArgs) -> anyhow::Result<&'static ProxyConfig> {
         timeout: Duration::from_secs(2),
     };
 
+    #[cfg(feature = "rest_broker")]
+    let rest_config = {
+        let db_schema_cache_config: CacheOptions = args.db_schema_cache.parse()?;
+        info!("Using DbSchemaCache with options={db_schema_cache_config:?}");
+
+        let db_schema_cache = if args.is_rest_broker {
+            Some(DbSchemaCache::new(
+                "db_schema_cache",
+                db_schema_cache_config.size,
+                db_schema_cache_config.ttl,
+                true,
+            ))
+        } else {
+            None
+        };
+
+        RestConfig {
+            is_rest_broker: args.is_rest_broker,
+            db_schema_cache,
+            max_schema_size: args.max_schema_size,
+            hostname_prefix: args.hostname_prefix.clone(),
+        }
+    };
+
     let config = ProxyConfig {
         tls_config,
         metric_collection,
@@ -691,6 +742,8 @@ fn build_config(args: &ProxyCliArgs) -> anyhow::Result<&'static ProxyConfig> {
         connect_to_compute: compute_config,
         #[cfg(feature = "testing")]
         disable_pg_session_jwt: false,
+        #[cfg(feature = "rest_broker")]
+        rest_config,
     };
 
     let config = Box::leak(Box::new(config));