diff --git a/src/shrpx_client_handler.cc b/src/shrpx_client_handler.cc
index 9b3ff083..a32c8e93 100644
--- a/src/shrpx_client_handler.cc
+++ b/src/shrpx_client_handler.cc
@@ -660,7 +660,7 @@ void ClientHandler::pool_downstream_connection(
 
   auto &shared_addr = group->shared_addr;
 
-  if (shared_addr->affinity.type == AFFINITY_NONE) {
+  if (shared_addr->affinity.type == SessionAffinity::NONE) {
     auto &dconn_pool = group->shared_addr->dconn_pool;
     dconn_pool.add_downstream_connection(std::move(dconn));
 
@@ -1003,17 +1003,17 @@ ClientHandler::get_downstream_connection(int &err, Downstream *downstream,
   auto &group = groups[group_idx];
   auto &shared_addr = group->shared_addr;
 
-  if (shared_addr->affinity.type != AFFINITY_NONE) {
+  if (shared_addr->affinity.type != SessionAffinity::NONE) {
     uint32_t hash;
     switch (shared_addr->affinity.type) {
-    case AFFINITY_IP:
+    case SessionAffinity::IP:
       if (!affinity_hash_computed_) {
         affinity_hash_ = compute_affinity_from_ip(ipaddr_);
         affinity_hash_computed_ = true;
       }
       hash = affinity_hash_;
       break;
-    case AFFINITY_COOKIE:
+    case SessionAffinity::COOKIE:
       hash = get_affinity_cookie(downstream, shared_addr->affinity.cookie.name);
       break;
     default:
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 76ffc55d..0b2ee031 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -903,11 +903,11 @@ int parse_downstream_params(DownstreamParams &out,
     } else if (util::istarts_with_l(param, "affinity=")) {
       auto valstr = StringRef{first + str_size("affinity="), end};
       if (util::strieq_l("none", valstr)) {
-        out.affinity.type = AFFINITY_NONE;
+        out.affinity.type = SessionAffinity::NONE;
       } else if (util::strieq_l("ip", valstr)) {
-        out.affinity.type = AFFINITY_IP;
+        out.affinity.type = SessionAffinity::IP;
       } else if (util::strieq_l("cookie", valstr)) {
-        out.affinity.type = AFFINITY_COOKIE;
+        out.affinity.type = SessionAffinity::COOKIE;
       } else {
         LOG(ERROR)
             << "backend: affinity: value must be one of none, ip, and cookie";
@@ -1004,7 +1004,7 @@ int parse_mapping(Config *config, DownstreamAddrConfig &addr,
     return -1;
   }
 
-  if (params.affinity.type == AFFINITY_COOKIE &&
+  if (params.affinity.type == SessionAffinity::COOKIE &&
       params.affinity.cookie.name.empty()) {
     LOG(ERROR) << "backend: affinity-cookie-name is mandatory if "
                   "affinity=cookie is specified";
@@ -1056,10 +1056,10 @@ int parse_mapping(Config *config, DownstreamAddrConfig &addr,
       auto &g = addr_groups[(*it).second];
       // Last value wins if we have multiple different affinity
       // value under one group.
-      if (params.affinity.type != AFFINITY_NONE) {
-        if (g.affinity.type == AFFINITY_NONE) {
+      if (params.affinity.type != SessionAffinity::NONE) {
+        if (g.affinity.type == SessionAffinity::NONE) {
           g.affinity.type = params.affinity.type;
-          if (params.affinity.type == AFFINITY_COOKIE) {
+          if (params.affinity.type == SessionAffinity::COOKIE) {
             g.affinity.cookie.name = make_string_ref(
                 downstreamconf.balloc, params.affinity.cookie.name);
             if (!params.affinity.cookie.path.empty()) {
@@ -1129,7 +1129,7 @@ int parse_mapping(Config *config, DownstreamAddrConfig &addr,
     auto &g = addr_groups.back();
     g.addrs.push_back(addr);
     g.affinity.type = params.affinity.type;
-    if (params.affinity.type == AFFINITY_COOKIE) {
+    if (params.affinity.type == SessionAffinity::COOKIE) {
       g.affinity.cookie.name =
           make_string_ref(downstreamconf.balloc, params.affinity.cookie.name);
       if (!params.affinity.cookie.path.empty()) {
@@ -4076,7 +4076,7 @@ int configure_downstream_group(Config *config, bool http2_proxy,
       }
     }
 
-    if (g.affinity.type != AFFINITY_NONE) {
+    if (g.affinity.type != SessionAffinity::NONE) {
       size_t idx = 0;
       for (auto &addr : g.addrs) {
         StringRef key;
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index ef2c1d61..d8476479 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -369,13 +369,13 @@ enum class Proto {
   MEMCACHED,
 };
 
-enum shrpx_session_affinity {
+enum class SessionAffinity {
   // No session affinity
-  AFFINITY_NONE,
+  NONE,
   // Client IP affinity
-  AFFINITY_IP,
+  IP,
   // Cookie based affinity
-  AFFINITY_COOKIE,
+  COOKIE,
 };
 
 enum shrpx_cookie_secure {
@@ -390,7 +390,7 @@ enum shrpx_cookie_secure {
 
 struct AffinityConfig {
   // Type of session affinity.
-  shrpx_session_affinity type;
+  SessionAffinity type;
   struct {
     // Name of a cookie to use.
     StringRef name;
@@ -496,13 +496,15 @@ struct AffinityHash {
 
 struct DownstreamAddrGroupConfig {
   DownstreamAddrGroupConfig(const StringRef &pattern)
-      : pattern(pattern), affinity{AFFINITY_NONE}, redirect_if_not_tls(false) {}
+      : pattern(pattern),
+        affinity{SessionAffinity::NONE},
+        redirect_if_not_tls(false) {}
 
   StringRef pattern;
   StringRef mruby_file;
   std::vector<DownstreamAddrConfig> addrs;
   // Bunch of session affinity hash.  Only used if affinity ==
-  // AFFINITY_IP.
+  // SessionAffinity::IP.
   std::vector<AffinityHash> affinity_hash;
   // Cookie based session affinity configuration.
   AffinityConfig affinity;
diff --git a/src/shrpx_http_downstream_connection.cc b/src/shrpx_http_downstream_connection.cc
index 8d035ee1..dac35824 100644
--- a/src/shrpx_http_downstream_connection.cc
+++ b/src/shrpx_http_downstream_connection.cc
@@ -259,7 +259,7 @@ int HttpDownstreamConnection::initiate_connection() {
     // initial_addr_idx_.
     size_t temp_idx = initial_addr_idx_;
 
-    auto &next_downstream = shared_addr->affinity.type == AFFINITY_NONE
+    auto &next_downstream = shared_addr->affinity.type == SessionAffinity::NONE
                                 ? shared_addr->next
                                 : temp_idx;
     auto end = next_downstream;
@@ -274,7 +274,7 @@ int HttpDownstreamConnection::initiate_connection() {
         assert(addr->dns);
       } else {
         assert(addr_ == nullptr);
-        if (shared_addr->affinity.type == AFFINITY_NONE) {
+        if (shared_addr->affinity.type == SessionAffinity::NONE) {
           addr = &addrs[next_downstream];
           if (++next_downstream >= addrs.size()) {
             next_downstream = 0;
@@ -810,7 +810,7 @@ void remove_from_pool(HttpDownstreamConnection *dconn) {
   auto &group = dconn->get_downstream_addr_group();
   auto &shared_addr = group->shared_addr;
 
-  if (shared_addr->affinity.type == AFFINITY_NONE) {
+  if (shared_addr->affinity.type == SessionAffinity::NONE) {
     auto &dconn_pool =
         dconn->get_downstream_addr_group()->shared_addr->dconn_pool;
     dconn_pool.remove_downstream_connection(dconn);
diff --git a/src/shrpx_worker.cc b/src/shrpx_worker.cc
index a321afc7..9ecdff00 100644
--- a/src/shrpx_worker.cc
+++ b/src/shrpx_worker.cc
@@ -77,7 +77,8 @@ DownstreamAddrGroup::~DownstreamAddrGroup() {}
 using DownstreamKey =
     std::tuple<std::vector<std::tuple<StringRef, StringRef, size_t, size_t,
                                       Proto, uint16_t, bool, bool, bool, bool>>,
-               bool, int, StringRef, StringRef, int, int64_t, int64_t>;
+               bool, SessionAffinity, StringRef, StringRef, int, int64_t,
+               int64_t>;
 
 namespace {
 DownstreamKey create_downstream_key(
@@ -164,7 +165,7 @@ void Worker::replace_downstream_config(
 
     auto &shared_addr = g->shared_addr;
 
-    if (shared_addr->affinity.type == AFFINITY_NONE) {
+    if (shared_addr->affinity.type == SessionAffinity::NONE) {
       shared_addr->dconn_pool.remove_all();
       continue;
     }
@@ -213,7 +214,7 @@ void Worker::replace_downstream_config(
 
     shared_addr->addrs.resize(src.addrs.size());
     shared_addr->affinity.type = src.affinity.type;
-    if (src.affinity.type == AFFINITY_COOKIE) {
+    if (src.affinity.type == SessionAffinity::COOKIE) {
       shared_addr->affinity.cookie.name =
           make_string_ref(shared_addr->balloc, src.affinity.cookie.name);
       if (!src.affinity.cookie.path.empty()) {
@@ -303,7 +304,7 @@ void Worker::replace_downstream_config(
       shared_addr->http1_pri.weight = num_http1;
       shared_addr->http2_pri.weight = num_http2;
 
-      if (shared_addr->affinity.type != AFFINITY_NONE) {
+      if (shared_addr->affinity.type != SessionAffinity::NONE) {
         for (auto &addr : shared_addr->addrs) {
           addr.dconn_pool = std::make_unique<DownstreamConnectionPool>();
         }
diff --git a/src/shrpx_worker.h b/src/shrpx_worker.h
index e5361725..f7d025ab 100644
--- a/src/shrpx_worker.h
+++ b/src/shrpx_worker.h
@@ -137,7 +137,7 @@ struct WeightedPri {
 struct SharedDownstreamAddr {
   SharedDownstreamAddr()
       : balloc(1024, 1024),
-        affinity{AFFINITY_NONE},
+        affinity{SessionAffinity::NONE},
         next{0},
         http1_pri{},
         http2_pri{},
@@ -151,7 +151,7 @@ struct SharedDownstreamAddr {
   BlockAllocator balloc;
   std::vector<DownstreamAddr> addrs;
   // Bunch of session affinity hash.  Only used if affinity ==
-  // AFFINITY_IP.
+  // SessionAffinity::IP.
   std::vector<AffinityHash> affinity_hash;
   // List of Http2Session which is not fully utilized (i.e., the
   // server advertised maximum concurrency is not reached).  We will