Make OSDs stick to the last successful etcd address

Previously OSDs were selecting a new random etcd from the cluster
on every request so they were failing randomly when part of etcds was down

src/etcd_state_client.cpp

@@ -50,19 +50,13 @@ void etcd_state_client_t::etcd_txn(json11::Json txn, int timeout, std::function<
 
 void etcd_state_client_t::etcd_call(std::string api, json11::Json payload, int timeout, std::function<void(std::string, json11::Json)> callback)
 {
-    if (!etcd_addresses.size())
+    if (!etcd_addresses.size() && !etcd_local.size())
     {
         fprintf(stderr, "etcd_address is missing in Vitastor configuration\n");
         exit(1);
     }
-    std::string etcd_address;
-    // Always prefer local etcd
-    // FIXME: Handle partial etcd failures. Now OSDs select etcd instance
-    // randomly so all OSDs may crash if any of etcds crashes.
-    if (etcd_local.size() > 0)
-        etcd_address = etcd_local[rand() % etcd_local.size()];
-    else
-        etcd_address = etcd_addresses[rand() % etcd_addresses.size()];
+    pick_next_etcd();
+    std::string etcd_address = selected_etcd_address;
     std::string etcd_api_path;
     int pos = etcd_address.find('/');
     if (pos >= 0)
@@ -77,7 +71,12 @@ void etcd_state_client_t::etcd_call(std::string api, json11::Json payload, int t
         "Content-Length: "+std::to_string(req.size())+"\r\n"
         "Connection: close\r\n"
         "\r\n"+req;
-    http_request_json(tfd, etcd_address, req, timeout, callback);
+    http_request_json(tfd, etcd_address, req, timeout, [this, cur_addr = selected_etcd_address, callback](std::string err, json11::Json data)
+    {
+        if (err != "" && cur_addr == selected_etcd_address)
+            selected_etcd_address = "";
+        callback(err, data);
+    });
 }
 
 void etcd_state_client_t::add_etcd_url(std::string addr)
@@ -104,10 +103,17 @@ void etcd_state_client_t::add_etcd_url(std::string addr)
             check_addr = addr;
         if (pos == std::string::npos)
             addr += "/v3";
-        this->etcd_addresses.push_back(addr);
-        for (int i = 0; i < local_ips.size(); i++)
+        int i;
+        for (i = 0; i < local_ips.size(); i++)
+        {
             if (local_ips[i] == check_addr)
+            {
                 this->etcd_local.push_back(addr);
+                break;
+            }
+        }
+        if (i >= local_ips.size())
+            this->etcd_addresses.push_back(addr);
     }
 }
 
@@ -146,14 +152,38 @@ void etcd_state_client_t::parse_config(const json11::Json & config)
     this->log_level = config["log_level"].int64_value();
 }
 
+void etcd_state_client_t::pick_next_etcd()
+{
+    if (selected_etcd_address != "")
+        return;
+    if (addresses_to_try.size() == 0)
+    {
+        // Prefer local etcd, if any
+        for (int i = 0; i < etcd_local.size(); i++)
+            addresses_to_try.push_back(etcd_local[i]);
+        std::vector<int> ns;
+        for (int i = 0; i < etcd_addresses.size(); i++)
+            ns.push_back(i);
+        while (ns.size())
+        {
+            int i = rand() % ns.size();
+            addresses_to_try.push_back(etcd_addresses[ns[i]]);
+            ns.erase(ns.begin()+i, ns.begin()+i+1);
+        }
+    }
+    selected_etcd_address = addresses_to_try[0];
+    addresses_to_try.erase(addresses_to_try.begin(), addresses_to_try.begin()+1);
+}
+
 void etcd_state_client_t::start_etcd_watcher()
 {
-    if (!etcd_addresses.size())
+    if (!etcd_addresses.size() && !etcd_local.size())
     {
         fprintf(stderr, "etcd_address is missing in Vitastor configuration\n");
         exit(1);
     }
-    std::string etcd_address = etcd_addresses[rand() % etcd_addresses.size()];
+    pick_next_etcd();
+    std::string etcd_address = selected_etcd_address;
     std::string etcd_api_path;
     int pos = etcd_address.find('/');
     if (pos >= 0)
@@ -162,7 +192,8 @@ void etcd_state_client_t::start_etcd_watcher()
         etcd_address = etcd_address.substr(0, pos);
     }
     etcd_watches_initialised = 0;
-    etcd_watch_ws = open_websocket(tfd, etcd_address, etcd_api_path+"/watch", ETCD_SLOW_TIMEOUT, [this](const http_response_t *msg)
+    etcd_watch_ws = open_websocket(tfd, etcd_address, etcd_api_path+"/watch", ETCD_SLOW_TIMEOUT,
+        [this, cur_addr = selected_etcd_address](const http_response_t *msg)
     {
         if (msg->body.length())
         {
@@ -181,6 +212,7 @@ void etcd_state_client_t::start_etcd_watcher()
                 if (etcd_watches_initialised == 4)
                 {
                     etcd_watch_revision = data["result"]["header"]["revision"].uint64_value();
+                    addresses_to_try.clear();
                 }
                 // First gather all changes into a hash to remove multiple overwrites
                 std::map<std::string, etcd_kv_t> changes;
@@ -209,11 +241,13 @@ void etcd_state_client_t::start_etcd_watcher()
         }
         if (msg->eof)
         {
+            if (cur_addr == selected_etcd_address)
+                selected_etcd_address = "";
             etcd_watch_ws = NULL;
             if (etcd_watches_initialised == 0)
             {
-                // Connection not established, retry in <ETCD_SLOW_TIMEOUT>
-                tfd->set_timer(ETCD_SLOW_TIMEOUT, false, [this](int)
+                // Connection not established, retry in <ETCD_QUICK_TIMEOUT>
+                tfd->set_timer(ETCD_QUICK_TIMEOUT, false, [this](int)
                 {
                     start_etcd_watcher();
                 });
@@ -805,3 +839,8 @@ json11::Json::object etcd_state_client_t::serialize_inode_cfg(inode_config_t *cf
     }
     return new_cfg;
 }
+
+int etcd_state_client_t::address_count()
+{
+    return etcd_addresses.size() + etcd_local.size();
+}