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/util/Cargo.toml

@@ -38,3 +38,6 @@ netapp = "0.3.0"
 
 http = "0.2"
 hyper = "0.14"
+
+kube = { version = "0.62", features = ["runtime", "derive"] }
+k8s-openapi = { version = "0.13", features = ["v1_22"] }

src/util/config.rs

@@ -52,6 +52,13 @@ pub struct Config {
 	pub consul_host: Option<String>,
 	/// Consul service name to use
 	pub consul_service_name: Option<String>,
+	/// Kubernetes namespace the service discovery resources are be created in
+	pub kubernetes_namespace: Option<String>,
+	/// Service name to filter for in k8s custom resources
+	pub kubernetes_service_name: Option<String>,
+	/// Skip creation of the garagenodes CRD
+	#[serde(default)]
+	pub kubernetes_skip_crd: bool,
 
 	/// Sled cache size, in bytes
 	#[serde(default = "default_sled_cache_capacity")]

src/util/error.rs

@@ -23,6 +23,9 @@ pub enum Error {
 	#[error(display = "Invalid HTTP header value: {}", _0)]
 	HttpHeader(#[error(source)] http::header::ToStrError),
 
+	#[error(display = "kubernetes error: {}", _0)]
+	Kubernetes(#[error(source)] kube::Error),
+
 	#[error(display = "Netapp error: {}", _0)]
 	Netapp(#[error(source)] netapp::error::Error),