add support for kubernetes service discovery

This commit adds support to discover garage instances running in
kubernetes.

Once enabled by setting `kubernetes_namespace` and
`kubernetes_service_name` garage will create a Custom Resources
`garagenodes.deuxfleurs.fr` with nodes public key as the resource name.
and IP and Port information as spec in the namespace configured by
`kubernetes_namespace`.

For discovering nodes the resources are filtered with the optionally set
`kubernetes_service_name` which sets a label
`garage.deuxfleurs.fr/service` on the resources.

This allows to separate multiple garage deployments in a single
namespace.

the `kubernetes_skip_crd` variable allows to disable the creation of the
CRD by garage itself. The user must deploy this manually.

src/rpc/system.rs

@@ -1,7 +1,7 @@
 //! Module containing structs related to membership management
 use std::collections::HashMap;
 use std::io::{Read, Write};
-use std::net::SocketAddr;
+use std::net::{IpAddr, SocketAddr};
 use std::path::Path;
 use std::sync::{Arc, RwLock};
 use std::time::{Duration, Instant};
@@ -29,6 +29,7 @@ use garage_util::persister::Persister;
 use garage_util::time::*;
 
 use crate::consul::*;
+use crate::kubernetes::*;
 use crate::layout::*;
 use crate::ring::*;
 use crate::rpc_helper::*;
@@ -88,6 +89,11 @@ pub struct System {
 	bootstrap_peers: Vec<(NodeID, SocketAddr)>,
 	consul_host: Option<String>,
 	consul_service_name: Option<String>,
+
+	kubernetes_service_name: Option<String>,
+	kubernetes_namespace: Option<String>,
+	kubernetes_skip_crd: bool,
+
 	replication_factor: usize,
 
 	/// The ring
@@ -247,6 +253,10 @@ impl System {
 			bootstrap_peers: config.bootstrap_peers.clone(),
 			consul_host: config.consul_host.clone(),
 			consul_service_name: config.consul_service_name.clone(),
+			kubernetes_service_name: config.kubernetes_service_name.clone(),
+			kubernetes_namespace: config.kubernetes_namespace.clone(),
+			kubernetes_skip_crd: config.kubernetes_skip_crd,
+
 			ring,
 			update_ring: Mutex::new(update_ring),
 			background,
@@ -295,6 +305,44 @@ impl System {
 		.err_context("Error while publishing Consul service")
 	}
 
+	fn get_default_ip() -> IpAddr {
+		pnet::datalink::interfaces()
+			.iter()
+			.find(|e| e.is_up() && !e.is_loopback() && !e.ips.is_empty())
+			.unwrap()
+			.ips
+			.first()
+			.unwrap()
+			.ip()
+	}
+
+	async fn advertise_to_kubernetes(self: Arc<Self>) -> Result<(), Error> {
+		let (kubernetes_service_name, kubernetes_namespace) =
+			match (&self.kubernetes_service_name, &self.kubernetes_namespace) {
+				(Some(ch), Some(csn)) => (ch, csn),
+				_ => return Ok(()),
+			};
+
+		let rpc_public_addr =
+			match self.rpc_public_addr {
+				Some(addr) => addr,
+				None => {
+					warn!("No rpc_public_addr configured, using first address on first network interface");
+					SocketAddr::new(Self::get_default_ip(), self.rpc_listen_addr.port())
+				}
+			};
+
+		publish_kubernetes_node(
+			kubernetes_service_name,
+			kubernetes_namespace,
+			self.netapp.id,
+			&self.local_status.load_full().hostname,
+			rpc_public_addr,
+		)
+		.await
+		.err_context("Error while publishing node to kubernetes")
+	}
+
 	/// Save network configuration to disc
 	async fn save_cluster_layout(self: Arc<Self>) -> Result<(), Error> {
 		let ring: Arc<Ring> = self.ring.borrow().clone();
@@ -470,6 +518,11 @@ impl System {
 			_ => None,
 		};
 
+		let kubernetes_config = match (&self.kubernetes_service_name, &self.kubernetes_namespace) {
+			(Some(ch), Some(csn)) => Some((ch.clone(), csn.clone())),
+			_ => None,
+		};
+
 		while !*stop_signal.borrow() {
 			let not_configured = !self.ring.borrow().layout.check();
 			let no_peers = self.fullmesh.get_peer_list().len() < self.replication_factor;
@@ -503,6 +556,28 @@ impl System {
 					}
 				}
 
+				// Fetch peer list from Kubernetes
+				if let Some((kubernetes_service_name, kubernetes_namespace)) = &kubernetes_config {
+					if !self.kubernetes_skip_crd {
+						match create_kubernetes_crd().await {
+							Ok(()) => (),
+							Err(e) => {
+								error!("Failed to create kubernetes custom resource: {}", e)
+							}
+						};
+					}
+
+					match get_kubernetes_nodes(kubernetes_service_name, kubernetes_namespace).await
+					{
+						Ok(node_list) => {
+							ping_list.extend(node_list);
+						}
+						Err(e) => {
+							warn!("Could not retrieve node list from Kubernetes: {}", e);
+						}
+					}
+				}
+
 				for (node_id, node_addr) in ping_list {
 					tokio::spawn(
 						self.netapp
@@ -518,6 +593,8 @@ impl System {
 			}
 
 			self.background.spawn(self.clone().advertise_to_consul());
+			self.background
+				.spawn(self.clone().advertise_to_kubernetes());
 
 			let restart_at = tokio::time::sleep(DISCOVERY_INTERVAL);
 			select! {