nghttpx: ConnectBlocker per backend address

src/shrpx_client_handler.cc

@@ -389,7 +389,7 @@ ClientHandler::ClientHandler(Worker *worker, int fd, SSL *ssl,
       pinned_http2sessions_(
           get_config()->conn.downstream.proto == PROTO_HTTP2
               ? make_unique<std::vector<ssize_t>>(
-                    get_config()->conn.downstream.addr_groups.size(), -1)
+                    worker->get_downstream_addr_groups().size(), -1)
               : nullptr),
       ipaddr_(ipaddr),
       port_(port),
@@ -664,8 +664,8 @@ std::unique_ptr<DownstreamConnection>
 ClientHandler::get_downstream_connection(Downstream *downstream) {
   size_t group;
   auto &downstreamconf = get_config()->conn.downstream;
-  auto &groups = downstreamconf.addr_groups;
   auto catch_all = downstreamconf.addr_group_catch_all;
+  auto &groups = worker_->get_downstream_addr_groups();
 
   const auto &req = downstream->request();
 
@@ -746,10 +746,6 @@ MemchunkPool *ClientHandler::get_mcpool() { return worker_->get_mcpool(); }
 
 SSL *ClientHandler::get_ssl() const { return conn_.tls.ssl; }
 
-ConnectBlocker *ClientHandler::get_connect_blocker() const {
-  return worker_->get_connect_blocker();
-}
-
 void ClientHandler::direct_http2_upgrade() {
   upstream_ = make_unique<Http2Upstream>(this);
   alpn_ = NGHTTP2_CLEARTEXT_PROTO_VERSION_ID;

src/shrpx_client_handler.h

@@ -99,7 +99,6 @@ public:
   get_downstream_connection(Downstream *downstream);
   MemchunkPool *get_mcpool();
   SSL *get_ssl() const;
-  ConnectBlocker *get_connect_blocker() const;
   // Call this function when HTTP/2 connection header is received at
   // the start of the connection.
   void direct_http2_upgrade();

src/shrpx_config.h

@@ -59,6 +59,7 @@ using namespace nghttp2;
 namespace shrpx {
 
 struct LogFragment;
+class ConnectBlocker;
 
 namespace ssl {
 
@@ -294,6 +295,7 @@ struct DownstreamAddr {
   // socket path.
   ImmutableString host;
   ImmutableString hostport;
+  ConnectBlocker *connect_blocker;
   // backend port.  0 if |host_unix| is true.
   uint16_t port;
   // true if |host| contains UNIX domain socket path.

src/shrpx_connect_blocker.cc

@@ -26,20 +26,16 @@
 
 namespace shrpx {
 
-namespace {
-const ev_tstamp INITIAL_SLEEP = 2.;
-} // namespace
-
 namespace {
 void connect_blocker_cb(struct ev_loop *loop, ev_timer *w, int revents) {
   if (LOG_ENABLED(INFO)) {
-    LOG(INFO) << "unblock downstream connection";
+    LOG(INFO) << "Unblock";
   }
 }
 } // namespace
 
-ConnectBlocker::ConnectBlocker(struct ev_loop *loop)
-    : loop_(loop), sleep_(INITIAL_SLEEP) {
+ConnectBlocker::ConnectBlocker(std::mt19937 &gen, struct ev_loop *loop)
+    : gen_(gen), loop_(loop), fail_count_(0) {
   ev_timer_init(&timer_, connect_blocker_cb, 0., 0.);
 }
 
@@ -47,18 +43,27 @@ ConnectBlocker::~ConnectBlocker() { ev_timer_stop(loop_, &timer_); }
 
 bool ConnectBlocker::blocked() const { return ev_is_active(&timer_); }
 
-void ConnectBlocker::on_success() { sleep_ = INITIAL_SLEEP; }
+void ConnectBlocker::on_success() { fail_count_ = 0; }
+
+namespace {
+constexpr size_t MAX_BACKOFF_EXP = 10;
+} // namespace
 
 void ConnectBlocker::on_failure() {
   if (ev_is_active(&timer_)) {
     return;
   }
 
-  sleep_ = std::min(128., sleep_ * 2);
+  ++fail_count_;
+
+  auto max_backoff = (1 << std::min(MAX_BACKOFF_EXP, fail_count_)) - 1;
+  auto dist = std::uniform_int_distribution<>(0, max_backoff);
+  auto backoff = dist(gen_);
 
-  LOG(WARN) << "connect failure, start sleeping " << sleep_;
+  LOG(WARN) << "Could not connect " << fail_count_
+            << " times in a row; sleep for " << backoff << " seconds";
 
-  ev_timer_set(&timer_, sleep_, 0.);
+  ev_timer_set(&timer_, backoff, 0.);
   ev_timer_start(loop_, &timer_);
 }
 

src/shrpx_connect_blocker.h

@@ -27,13 +27,15 @@
 
 #include "shrpx.h"
 
+#include <random>
+
 #include <ev.h>
 
 namespace shrpx {
 
 class ConnectBlocker {
 public:
-  ConnectBlocker(struct ev_loop *loop);
+  ConnectBlocker(std::mt19937 &gen, struct ev_loop *loop);
   ~ConnectBlocker();
 
   // Returns true if making connection is not allowed.
@@ -41,14 +43,18 @@ public:
   // Call this function if connect operation succeeded.  This will
   // reset sleep_ to minimum value.
   void on_success();
-  // Call this function if connect operation failed.  This will start
-  // timer and blocks connection establishment for sleep_ seconds.
+  // Call this function if connect operations failed.  This will start
+  // timer and blocks connection establishment with exponential
+  // backoff.
   void on_failure();
 
 private:
+  std::mt19937 gen_;
   ev_timer timer_;
   struct ev_loop *loop_;
-  ev_tstamp sleep_;
+  // The number of consecutive connection failure.  Reset to 0 on
+  // success.
+  size_t fail_count_;
 };
 
 } // namespace

src/shrpx_http2_downstream_connection.cc

@@ -98,6 +98,9 @@ int Http2DownstreamConnection::attach_downstream(Downstream *downstream) {
   http2session_->add_downstream_connection(this);
   if (http2session_->get_state() == Http2Session::DISCONNECTED) {
     http2session_->signal_write();
+    if (http2session_->get_state() == Http2Session::DISCONNECTED) {
+      return -1;
+    }
   }
 
   downstream_ = downstream;

src/shrpx_http2_session.cc

@@ -147,8 +147,7 @@ void writecb(struct ev_loop *loop, ev_io *w, int revents) {
 } // namespace
 
 Http2Session::Http2Session(struct ev_loop *loop, SSL_CTX *ssl_ctx,
-                           ConnectBlocker *connect_blocker, Worker *worker,
-                           size_t group, size_t idx)
+                           Worker *worker, size_t group, size_t idx)
     : conn_(loop, -1, nullptr, worker->get_mcpool(),
             get_config()->conn.downstream.timeout.write,
             get_config()->conn.downstream.timeout.read, {}, {}, writecb, readcb,
@@ -156,7 +155,6 @@ Http2Session::Http2Session(struct ev_loop *loop, SSL_CTX *ssl_ctx,
             get_config()->tls.dyn_rec.idle_timeout),
       wb_(worker->get_mcpool()),
       worker_(worker),
-      connect_blocker_(connect_blocker),
       ssl_ctx_(ssl_ctx),
       addr_(nullptr),
       session_(nullptr),
@@ -254,30 +252,49 @@ int Http2Session::disconnect(bool hard) {
 int Http2Session::initiate_connection() {
   int rv = 0;
 
-  auto &addrs = get_config()->conn.downstream.addr_groups[group_].addrs;
+  auto &groups = worker_->get_downstream_addr_groups();
+  auto &addrs = groups[group_].addrs;
 
   if (state_ == DISCONNECTED) {
-    if (connect_blocker_->blocked()) {
-      if (LOG_ENABLED(INFO)) {
-        DCLOG(INFO, this)
-            << "Downstream connection was blocked by connect_blocker";
+    auto &next_downstream = worker_->get_dgrp(group_)->next;
+    auto end = next_downstream;
+
+    for (;;) {
+      auto &addr = addrs[next_downstream];
+
+      if (++next_downstream >= addrs.size()) {
+        next_downstream = 0;
       }
-      return -1;
-    }
 
-    auto &next_downstream = worker_->get_dgrp(group_)->next;
-    addr_ = &addrs[next_downstream];
+      auto &connect_blocker = addr.connect_blocker;
 
-    if (LOG_ENABLED(INFO)) {
-      SSLOG(INFO, this) << "Using downstream address idx=" << next_downstream
-                        << " out of " << addrs.size();
-    }
+      if (connect_blocker->blocked()) {
+        if (LOG_ENABLED(INFO)) {
+          DCLOG(INFO, this) << "Backend server "
+                            << (addr.host_unix ? addr.host : addr.hostport)
+                            << " was not available temporarily";
+        }
+
+        if (end == next_downstream) {
+          return -1;
+        }
+
+        continue;
+      }
+
+      if (LOG_ENABLED(INFO)) {
+        SSLOG(INFO, this) << "Using downstream address idx=" << next_downstream
+                          << " out of " << addrs.size();
+      }
+
+      addr_ = &addr;
 
-    if (++next_downstream >= addrs.size()) {
-      next_downstream = 0;
+      break;
     }
   }
 
+  auto &connect_blocker = addr_->connect_blocker;
+
   const auto &proxy = get_config()->downstream_http_proxy;
   if (!proxy.host.empty() && state_ == DISCONNECTED) {
     if (LOG_ENABLED(INFO)) {
@@ -288,7 +305,7 @@ int Http2Session::initiate_connection() {
     conn_.fd = util::create_nonblock_socket(proxy.addr.su.storage.ss_family);
 
     if (conn_.fd == -1) {
-      connect_blocker_->on_failure();
+      connect_blocker->on_failure();
       return -1;
     }
 
@@ -296,7 +313,7 @@ int Http2Session::initiate_connection() {
     if (rv != 0 && errno != EINPROGRESS) {
       SSLOG(ERROR, this) << "Failed to connect to the proxy " << proxy.host
                          << ":" << proxy.port;
-      connect_blocker_->on_failure();
+      connect_blocker->on_failure();
       return -1;
     }
 
@@ -356,7 +373,7 @@ int Http2Session::initiate_connection() {
         conn_.fd =
             util::create_nonblock_socket(addr_->addr.su.storage.ss_family);
         if (conn_.fd == -1) {
-          connect_blocker_->on_failure();
+          connect_blocker->on_failure();
           return -1;
         }
 
@@ -365,7 +382,7 @@ int Http2Session::initiate_connection() {
                      const_cast<sockaddr *>(&addr_->addr.su.sa),
                      addr_->addr.len);
         if (rv != 0 && errno != EINPROGRESS) {
-          connect_blocker_->on_failure();
+          connect_blocker->on_failure();
           return -1;
         }
 
@@ -383,14 +400,14 @@ int Http2Session::initiate_connection() {
             util::create_nonblock_socket(addr_->addr.su.storage.ss_family);
 
         if (conn_.fd == -1) {
-          connect_blocker_->on_failure();
+          connect_blocker->on_failure();
           return -1;
         }
 
         rv = connect(conn_.fd, const_cast<sockaddr *>(&addr_->addr.su.sa),
                      addr_->addr.len);
         if (rv != 0 && errno != EINPROGRESS) {
-          connect_blocker_->on_failure();
+          connect_blocker->on_failure();
           return -1;
         }
 
@@ -1615,11 +1632,15 @@ int Http2Session::read_noop(const uint8_t *data, size_t datalen) { return 0; }
 int Http2Session::write_noop() { return 0; }
 
 int Http2Session::connected() {
+  auto &connect_blocker = addr_->connect_blocker;
+
   if (!util::check_socket_connected(conn_.fd)) {
+    connect_blocker->on_failure();
+
     return -1;
   }
 
-  connect_blocker_->on_success();
+  connect_blocker->on_success();
 
   if (LOG_ENABLED(INFO)) {
     SSLOG(INFO, this) << "Connection established";

src/shrpx_http2_session.h

@@ -48,7 +48,6 @@ namespace shrpx {
 
 class Http2DownstreamConnection;
 class Worker;
-class ConnectBlocker;
 
 struct StreamData {
   StreamData *dlnext, *dlprev;
@@ -57,9 +56,8 @@ struct StreamData {
 
 class Http2Session {
 public:
-  Http2Session(struct ev_loop *loop, SSL_CTX *ssl_ctx,
-               ConnectBlocker *connect_blocker, Worker *worker, size_t group,
-               size_t idx);
+  Http2Session(struct ev_loop *loop, SSL_CTX *ssl_ctx, Worker *worker,
+               size_t group, size_t idx);
   ~Http2Session();
 
   // If hard is true, all pending requests are abandoned and
@@ -203,7 +201,6 @@ private:
   // Used to parse the response from HTTP proxy
   std::unique_ptr<http_parser> proxy_htp_;
   Worker *worker_;
-  ConnectBlocker *connect_blocker_;
   // NULL if no TLS is configured
   SSL_CTX *ssl_ctx_;
   // Address of remote endpoint

src/shrpx_http_downstream_connection.cc

@@ -147,16 +147,6 @@ int HttpDownstreamConnection::attach_downstream(Downstream *downstream) {
   auto &downstreamconf = get_config()->conn.downstream;
 
   if (conn_.fd == -1) {
-    auto connect_blocker = client_handler_->get_connect_blocker();
-
-    if (connect_blocker->blocked()) {
-      if (LOG_ENABLED(INFO)) {
-        DCLOG(INFO, this)
-            << "Downstream connection was blocked by connect_blocker";
-      }
-      return -1;
-    }
-
     if (ssl_ctx_) {
       auto ssl = ssl::create_ssl(ssl_ctx_);
       if (!ssl) {
@@ -168,7 +158,8 @@ int HttpDownstreamConnection::attach_downstream(Downstream *downstream) {
 
     auto &next_downstream = worker_->get_dgrp(group_)->next;
     auto end = next_downstream;
-    auto &addrs = downstreamconf.addr_groups[group_].addrs;
+    auto &groups = worker_->get_downstream_addr_groups();
+    auto &addrs = groups[group_].addrs;
     for (;;) {
       auto &addr = addrs[next_downstream];
 
@@ -176,6 +167,22 @@ int HttpDownstreamConnection::attach_downstream(Downstream *downstream) {
         next_downstream = 0;
       }
 
+      auto &connect_blocker = addr.connect_blocker;
+
+      if (connect_blocker->blocked()) {
+        if (LOG_ENABLED(INFO)) {
+          DCLOG(INFO, this) << "Backend server "
+                            << (addr.host_unix ? addr.host : addr.hostport)
+                            << " was not available temporarily";
+        }
+
+        if (end == next_downstream) {
+          return SHRPX_ERR_NETWORK;
+        }
+
+        continue;
+      }
+
       conn_.fd = util::create_nonblock_socket(addr.addr.su.storage.ss_family);
 
       if (conn_.fd == -1) {
@@ -1012,7 +1019,7 @@ int HttpDownstreamConnection::process_input(const uint8_t *data,
 }
 
 int HttpDownstreamConnection::connected() {
-  auto connect_blocker = client_handler_->get_connect_blocker();
+  auto connect_blocker = addr_->connect_blocker;
 
   if (!util::check_socket_connected(conn_.fd)) {
     conn_.wlimit.stopw();
@@ -1021,6 +1028,8 @@ int HttpDownstreamConnection::connected() {
       DLOG(INFO, this) << "downstream connect failed";
     }
 
+    connect_blocker->on_failure();
+
     downstream_->set_request_state(Downstream::CONNECT_FAIL);
 
     return -1;

src/shrpx_worker.cc

@@ -80,7 +80,7 @@ Worker::Worker(struct ev_loop *loop, SSL_CTX *sv_ssl_ctx, SSL_CTX *cl_ssl_ctx,
       cl_ssl_ctx_(cl_ssl_ctx),
       cert_tree_(cert_tree),
       ticket_keys_(ticket_keys),
-      connect_blocker_(make_unique<ConnectBlocker>(loop_)),
+      downstream_addr_groups_(get_config()->conn.downstream.addr_groups),
       graceful_shutdown_(false) {
   ev_async_init(&w_, eventcb);
   w_.data = this;
@@ -109,17 +109,29 @@ Worker::Worker(struct ev_loop *loop, SSL_CTX *sv_ssl_ctx, SSL_CTX *cl_ssl_ctx,
         m = downstreamconf.addr_groups[group].addrs.size();
       }
       for (size_t idx = 0; idx < m; ++idx) {
-        dgrp.http2sessions.push_back(make_unique<Http2Session>(
-            loop_, cl_ssl_ctx, connect_blocker_.get(), this, group, idx));
+        dgrp.http2sessions.push_back(
+            make_unique<Http2Session>(loop_, cl_ssl_ctx, this, group, idx));
       }
       ++group;
     }
   }
+
+  for (auto &group : downstream_addr_groups_) {
+    for (auto &addr : group.addrs) {
+      addr.connect_blocker = new ConnectBlocker(randgen_, loop_);
+    }
+  }
 }
 
 Worker::~Worker() {
   ev_async_stop(loop_, &w_);
   ev_timer_stop(loop_, &mcpool_clear_timer_);
+
+  for (auto &group : downstream_addr_groups_) {
+    for (auto &addr : group.addrs) {
+      delete addr.connect_blocker;
+    }
+  }
 }
 
 void Worker::schedule_clear_mcpool() {
@@ -259,10 +271,6 @@ Http2Session *Worker::next_http2_session(size_t group) {
   return res;
 }
 
-ConnectBlocker *Worker::get_connect_blocker() const {
-  return connect_blocker_.get();
-}
-
 struct ev_loop *Worker::get_loop() const {
   return loop_;
 }
@@ -361,4 +369,8 @@ SSL_SESSION *Worker::reuse_client_tls_session(const Address *addr) {
   return d2i_SSL_SESSION(nullptr, &p, ent.session_data.size());
 }
 
+std::vector<DownstreamAddrGroup> &Worker::get_downstream_addr_groups() {
+  return downstream_addr_groups_;
+}
+
 } // namespace shrpx

src/shrpx_worker.h

@@ -131,7 +131,6 @@ public:
   WorkerStat *get_worker_stat();
   DownstreamConnectionPool *get_dconn_pool();
   Http2Session *next_http2_session(size_t group);
-  ConnectBlocker *get_connect_blocker() const;
   struct ev_loop *get_loop() const;
   SSL_CTX *get_sv_ssl_ctx() const;
   SSL_CTX *get_cl_ssl_ctx() const;
@@ -164,6 +163,8 @@ public:
   // found associated to |addr|, nullptr will be returned.
   SSL_SESSION *reuse_client_tls_session(const Address *addr);
 
+  std::vector<DownstreamAddrGroup> &get_downstream_addr_groups();
+
 private:
 #ifndef NOTHREADS
   std::future<void> fut_;
@@ -196,7 +197,7 @@ private:
   ssl::CertLookupTree *cert_tree_;
 
   std::shared_ptr<TicketKeys> ticket_keys_;
-  std::unique_ptr<ConnectBlocker> connect_blocker_;
+  std::vector<DownstreamAddrGroup> downstream_addr_groups_;
 
   bool graceful_shutdown_;
 };