diff --git a/src/app/config/config.c b/src/app/config/config.c
index bbf984ad08..57aa055e73 100644
--- a/src/app/config/config.c
+++ b/src/app/config/config.c
@@ -510,6 +510,8 @@ static const config_var_t option_vars_[] = {
       LINELIST_S, RendConfigLines, NULL),
   VAR("HiddenServiceEnableIntroDoSBurstPerSec",
       LINELIST_S, RendConfigLines, NULL),
+  VAR("HiddenServiceOnionBalanceInstance",
+      LINELIST_S, RendConfigLines, NULL),
   VAR("HiddenServiceStatistics", BOOL, HiddenServiceStatistics_option, "1"),
   V(HidServAuth,                 LINELIST, NULL),
   V(ClientOnionAuthDir,          FILENAME, NULL),
diff --git a/src/feature/hs/hs_config.c b/src/feature/hs/hs_config.c
index 64656b1935..684f7bc975 100644
--- a/src/feature/hs/hs_config.c
+++ b/src/feature/hs/hs_config.c
@@ -26,6 +26,7 @@
 #include "feature/hs/hs_common.h"
 #include "feature/hs/hs_config.h"
 #include "feature/hs/hs_client.h"
+#include "feature/hs/hs_ob.h"
 #include "feature/hs/hs_service.h"
 #include "feature/rend/rendclient.h"
 #include "feature/rend/rendservice.h"
@@ -219,6 +220,7 @@ config_has_invalid_options(const config_line_t *line_,
     "HiddenServiceEnableIntroDoSDefense",
     "HiddenServiceEnableIntroDoSRatePerSec",
     "HiddenServiceEnableIntroDoSBurstPerSec",
+    "HiddenServiceOnionBalanceInstance",
     NULL /* End marker. */
   };
 
@@ -317,7 +319,7 @@ config_service_v3(const config_line_t *line_,
   int have_num_ip = 0;
   bool export_circuit_id = false; /* just to detect duplicate options */
   bool dos_enabled = false, dos_rate_per_sec = false;
-  bool dos_burst_per_sec = false;
+  bool dos_burst_per_sec = false, ob_instance = false;
   const char *dup_opt_seen = NULL;
   const config_line_t *line;
 
@@ -402,6 +404,27 @@ config_service_v3(const config_line_t *line_,
                config->intro_dos_burst_per_sec);
       continue;
     }
+    if (!strcasecmp(line->key, "HiddenServiceOnionBalanceInstance")) {
+      bool enabled = !!helper_parse_uint64(line->key, line->value,
+                                           0, 1, &ok);
+      if (!ok || ob_instance) {
+        if (ob_instance) {
+          dup_opt_seen = line->key;
+        }
+        goto err;
+      }
+      ob_instance = true;
+      if (!enabled) {
+        /* Skip if this is disabled. */
+        continue;
+      }
+      /* Option is enabled, parse config file. */
+      ok = hs_ob_parse_config_file(config);
+      if (!ok) {
+        goto err;
+      }
+      continue;
+    }
   }
 
   /* We do not load the key material for the service at this stage. This is
diff --git a/src/feature/hs/hs_ob.c b/src/feature/hs/hs_ob.c
new file mode 100644
index 0000000000..633b157a09
--- /dev/null
+++ b/src/feature/hs/hs_ob.c
@@ -0,0 +1,222 @@
+/* Copyright (c) 2017-2020, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file hs_ob.c
+ * \brief Implement Onion Balance specific code.
+ *
+ * \details
+ *
+ * XXX:
+ **/
+
+#define HS_OB_PRIVATE
+
+#include "lib/confmgt/confmgt.h"
+#include "lib/encoding/confline.h"
+
+#include "hs_ob.h"
+
+/* Options config magic number. */
+#define OB_OPTIONS_MAGIC 0x631DE7EA
+
+/* Helper macros. */
+#define VAR(varname, conftype, member, initvalue)                          \
+  CONFIG_VAR_ETYPE(ob_options_t, varname, conftype, member, 0, initvalue)
+#define V(member,conftype,initvalue)        \
+  VAR(#member, conftype, member, initvalue)
+
+/* Dummy instance of ob_options_t, used for type-checking its members with
+ * CONF_CHECK_VAR_TYPE. */
+DUMMY_TYPECHECK_INSTANCE(ob_options_t);
+
+/* Array of variables for the config file options. */
+static const config_var_t config_vars[] = {
+  V(MasterOnionAddress, LINELIST, NULL),
+
+  END_OF_CONFIG_VARS
+};
+
+/* "Extra" variable in the state that receives lines we can't parse. This
+ * lets us preserve options from versions of Tor newer than us. */
+static const struct_member_t config_extra_vars = {
+  .name = "__extra",
+  .type = CONFIG_TYPE_LINELIST,
+  .offset = offsetof(ob_options_t, ExtraLines),
+};
+
+/* Configuration format of ob_options_t. */
+static const config_format_t config_format = {
+  .size = sizeof(ob_options_t),
+  .magic = {
+     "ob_options_t",
+     OB_OPTIONS_MAGIC,
+     offsetof(ob_options_t, magic_),
+  },
+  .vars = config_vars,
+  .extra = &config_extra_vars,
+};
+
+/* Global configuration manager for the config file. */
+static config_mgr_t *config_options_mgr = NULL;
+
+/* Return the configuration manager for the config file. */
+static const config_mgr_t *
+get_config_options_mgr(void)
+{
+  if (PREDICT_UNLIKELY(config_options_mgr == NULL)) {
+    config_options_mgr = config_mgr_new(&config_format);
+    config_mgr_freeze(config_options_mgr);
+  }
+  return config_options_mgr;
+}
+
+#define ob_option_free(val) \
+  FREE_AND_NULL(ob_options_t, ob_option_free_, (val))
+
+/** Helper: Free a config options object. */
+static void
+ob_option_free_(ob_options_t *opts)
+{
+  if (opts == NULL) {
+    return;
+  }
+  config_free(get_config_options_mgr(), opts);
+}
+
+/** Return an allocated config options object. */
+static ob_options_t *
+ob_option_new(void)
+{
+  ob_options_t *opts = config_new(get_config_options_mgr());
+  config_init(get_config_options_mgr(), opts);
+  return opts;
+}
+
+/** Helper function: From the configuration line value which is an onion
+ * address with the ".onion" extension, find the public key and put it in
+ * pkey_out.
+ *
+ * On success, true is returned. Else, false and pkey is untouched. */
+static bool
+get_onion_public_key(const char *value, ed25519_public_key_t *pkey_out)
+{
+  char address[HS_SERVICE_ADDR_LEN_BASE32 + 1];
+
+  tor_assert(value);
+  tor_assert(pkey_out);
+
+  if (strcmpend(value, ".onion")) {
+    /* Not a .onion extension, bad format. */
+    return false;
+  }
+
+  /* Length validation. The -1 is because sizeof() counts the NUL byte. */
+  if (strlen(value) >
+      (HS_SERVICE_ADDR_LEN_BASE32 + sizeof(".onion") - 1)) {
+    /* Too long, bad format. */
+    return false;
+  }
+
+  /* We don't want the .onion so we add 2 because size - 1 is copied with
+   * strlcpy() in order to accomodate the NUL byte and sizeof() counts the NUL
+   * byte so we need to remove them from the equation. */
+  strlcpy(address, value, strlen(value) - sizeof(".onion") + 2);
+
+  if (hs_parse_address_no_log(address, pkey_out, NULL, NULL, NULL) < 0) {
+    return false;
+  }
+
+  /* Success. */
+  return true;
+}
+
+/** Parse the given ob options in opts and set the service config object
+ * accordingly.
+ *
+ * Return 1 on success else 0. */
+static int
+ob_option_parse(hs_service_config_t *config, const ob_options_t *opts)
+{
+  int ret = 0;
+  config_line_t *line;
+
+  tor_assert(config);
+  tor_assert(opts);
+
+  for (line = opts->MasterOnionAddress; line; line = line->next) {
+    /* Allocate config list if need be. */
+    if (!config->ob_master_pubkeys) {
+      config->ob_master_pubkeys = smartlist_new();
+    }
+    ed25519_public_key_t *pubkey = tor_malloc_zero(sizeof(*pubkey));
+
+    if (!get_onion_public_key(line->value, pubkey)) {
+      log_warn(LD_REND, "OnionBalance: MasterOnionAddress %s is invalid",
+               line->value);
+      tor_free(pubkey);
+      goto end;
+    }
+    smartlist_add(config->ob_master_pubkeys, pubkey);
+  }
+  /* Success. */
+  ret = 1;
+
+ end:
+  /* No keys added, we free the list since no list means no onion balance
+   * support for this tor instance. */
+  if (smartlist_len(config->ob_master_pubkeys) == 0) {
+    smartlist_free(config->ob_master_pubkeys);
+  }
+  return ret;
+}
+
+/** Read and parse the config file at fname on disk. The service config object
+ * is populated with the options if any.
+ *
+ * Return 1 on success else 0. This is to follow the "ok" convention in
+ * hs_config.c. */
+int
+hs_ob_parse_config_file(hs_service_config_t *config)
+{
+  static const char *fname = "ob_config";
+  int ret = 0;
+  char *content = NULL, *errmsg = NULL, *config_file_path = NULL;
+  ob_options_t *options = NULL;
+  config_line_t *lines = NULL;
+
+  tor_assert(config);
+
+  /* Read file from disk. */
+  config_file_path = hs_path_from_filename(config->directory_path, fname);
+  content = read_file_to_str(config_file_path, 0, NULL);
+  if (!content) {
+    log_warn(LD_FS, "OnionBalance: Unable to read config file %s",
+             escaped(config_file_path));
+    goto end;
+  }
+
+  /* Parse lines. */
+  if (config_get_lines(content, &lines, 0) < 0) {
+    goto end;
+  }
+
+  options = ob_option_new();
+  config_assign(get_config_options_mgr(), options, lines, 0, &errmsg);
+  if (errmsg) {
+    log_warn(LD_REND, "OnionBalance: Unable to parse config file: %s",
+             errmsg);
+    tor_free(errmsg);
+    goto end;
+  }
+
+  /* Parse the options and set the service config object with the details. */
+  ret = ob_option_parse(config, options);
+
+ end:
+  config_free_lines(lines);
+  ob_option_free(options);
+  tor_free(content);
+  tor_free(config_file_path);
+  return ret;
+}
diff --git a/src/feature/hs/hs_ob.h b/src/feature/hs/hs_ob.h
new file mode 100644
index 0000000000..d16896f2ed
--- /dev/null
+++ b/src/feature/hs/hs_ob.h
@@ -0,0 +1,29 @@
+/* Copyright (c) 2020, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file hs_ob.h
+ * \brief Header file for the specific code for onion balance.
+ **/
+
+#ifndef TOR_HS_OB_H
+#define TOR_HS_OB_H
+
+#include "hs_service.h"
+
+int hs_ob_parse_config_file(hs_service_config_t *config);
+
+#ifdef HS_OB_PRIVATE
+
+typedef struct ob_options_t {
+  /** Magic number to identify the structure in memory. */
+  uint32_t magic_;
+  /** Master Onion Address(es). */
+  struct config_line_t *MasterOnionAddress;
+  /** Extra Lines for configuration we might not know. */
+  struct config_line_t *ExtraLines;
+} ob_options_t;
+
+#endif /* defined(HS_OB_PRIVATE) */
+
+#endif /* !defined(TOR_HS_OB_H) */
diff --git a/src/feature/hs/hs_service.c b/src/feature/hs/hs_service.c
index 81b37eab40..d0d9d65790 100644
--- a/src/feature/hs/hs_service.c
+++ b/src/feature/hs/hs_service.c
@@ -267,6 +267,11 @@ service_clear_config(hs_service_config_t *config)
                       service_authorized_client_free(p));
     smartlist_free(config->clients);
   }
+  if (config->ob_master_pubkeys) {
+    SMARTLIST_FOREACH(config->ob_master_pubkeys, ed25519_public_key_t *, k,
+                      tor_free(k));
+    smartlist_free(config->ob_master_pubkeys);
+  }
   memset(config, 0, sizeof(*config));
 }
 
diff --git a/src/feature/hs/hs_service.h b/src/feature/hs/hs_service.h
index 8809411e01..bdc2bc3b64 100644
--- a/src/feature/hs/hs_service.h
+++ b/src/feature/hs/hs_service.h
@@ -248,10 +248,14 @@ typedef struct hs_service_config_t {
   /** Does this service export the circuit ID of its clients? */
   hs_circuit_id_protocol_t circuit_id_protocol;
 
-  /* DoS defenses. For the ESTABLISH_INTRO cell extension. */
+  /** DoS defenses. For the ESTABLISH_INTRO cell extension. */
   unsigned int has_dos_defense_enabled : 1;
   uint32_t intro_dos_rate_per_sec;
   uint32_t intro_dos_burst_per_sec;
+
+  /** If set, contains the Onion Balance master ed25519 public key (taken from
+   * an .onion addresses) that this tor instance serves as backend. */
+  smartlist_t *ob_master_pubkeys;
 } hs_service_config_t;
 
 /** Service state. */
diff --git a/src/feature/hs/include.am b/src/feature/hs/include.am
index 5e69607e59..f83907c76b 100644
--- a/src/feature/hs/include.am
+++ b/src/feature/hs/include.am
@@ -13,6 +13,7 @@ LIBTOR_APP_A_SOURCES += 				\
 	src/feature/hs/hs_dos.c			\
 	src/feature/hs/hs_ident.c		\
 	src/feature/hs/hs_intropoint.c		\
+	src/feature/hs/hs_ob.c			\
 	src/feature/hs/hs_service.c		\
 	src/feature/hs/hs_stats.c
 
@@ -30,6 +31,7 @@ noinst_HEADERS +=					\
 	src/feature/hs/hs_dos.h				\
 	src/feature/hs/hs_ident.h			\
 	src/feature/hs/hs_intropoint.h			\
+	src/feature/hs/hs_ob.h				\
 	src/feature/hs/hs_service.h			\
 	src/feature/hs/hs_stats.h			\
 	src/feature/hs/hsdir_index_st.h