storage: add mirror health checking support

api/src/http.rs

@@ -400,6 +400,7 @@ impl Default for ProxyConfig {
 
 /// Configuration for mirror.
 #[derive(Clone, Deserialize, Serialize, Debug)]
+#[serde(default)]
 pub struct MirrorConfig {
     /// Mirror server URL, for example http://127.0.0.1:65001.
     pub host: String,
@@ -412,6 +413,28 @@ pub struct MirrorConfig {
     /// e.g. when using Dragonfly server as mirror, authorization through it will affect performance.
     #[serde(default)]
     pub auth_through: bool,
+    /// Interval of mirror health checking, in seconds.
+    #[serde(default = "default_check_interval")]
+    pub health_check_interval: u64,
+    /// Failure count for which mirror is considered unavailable.
+    #[serde(default = "default_failure_limit")]
+    pub failure_limit: u8,
+    /// Ping URL to check mirror server health.
+    #[serde(default)]
+    pub ping_url: String,
+}
+
+impl Default for MirrorConfig {
+    fn default() -> Self {
+        Self {
+            host: String::new(),
+            headers: HashMap::new(),
+            auth_through: false,
+            health_check_interval: 5,
+            failure_limit: 5,
+            ping_url: String::new(),
+        }
+    }
 }
 
 #[derive(Debug)]
@@ -623,6 +646,14 @@ fn default_http_timeout() -> u32 {
     5
 }
 
+fn default_check_interval() -> u64 {
+    5
+}
+
+fn default_failure_limit() -> u8 {
+    5
+}
+
 fn default_work_dir() -> String {
     ".".to_string()
 }

docs/nydusd.md

@@ -265,13 +265,21 @@ Currently, the mirror mode is only tested in the registry backend, and in theory
               // When Dragonfly does not cache data, nydusd will pull it from "X-Dragonfly-Registry".
               // If not set "X-Dragonfly-Registry", Dragonfly will pull data from proxy.registryMirror.url.
               "X-Dragonfly-Registry": "https://index.docker.io"
-            }
+            },
+            // This URL endpoint is used to check the health of mirror server, and if the mirror is unhealthy, 
+            // the request will fallback to the next mirror or the original registry server. 
+            // Use $host/v2 as default if left empty.
+            "ping_url": "http://127.0.0.1:40901/server/ping",
+            // Interval time (s) to check and recover unavailable mirror. Use 5 as default if left empty.
+            "health_check_interval": 5,
+            // Failure counts before disabling this mirror. Use 5 as default if left empty.
+            "failure_limit": 5,
           },
           {
             "host": "http://dragonfly2.io:65001",
             "headers": {
               "X-Dragonfly-Registry": "https://index.docker.io"
-            }
+            },
           }
         ],
         ...