Merge pull request #8961 from Icinga/bugfix/apilistener-detect-ipv6-support

ApiListener: Choose bind host default based on OS IPv6 support (2.13)

Author: N-o-X

doc/09-object-types.md

@@ -1095,7 +1095,7 @@ Configuration Attributes:
   ca\_path                              | String                | **Deprecated.** Path to the CA certificate file.
   ticket\_salt                          | String                | **Optional.** Private key for [CSR auto-signing](06-distributed-monitoring.md#distributed-monitoring-setup-csr-auto-signing). **Required** for a signing master instance.
   crl\_path                             | String                | **Optional.** Path to the CRL file.
-  bind\_host                            | String                | **Optional.** The IP address the api listener should be bound to. If not specified, the ApiListener is bound to `::` and listens for both IPv4 and IPv6 connections.
+  bind\_host                            | String                | **Optional.** The IP address the api listener should be bound to. If not specified, the ApiListener is bound to `::` and listens for both IPv4 and IPv6 connections or to `0.0.0.0` if IPv6 is not supported by the operating system.
   bind\_port                            | Number                | **Optional.** The port the api listener should be bound to. Defaults to `5665`.
   accept\_config                        | Boolean               | **Optional.** Accept zone configuration. Defaults to `false`.
   accept\_commands                      | Boolean               | **Optional.** Accept remote commands. Defaults to `false`.

doc/17-language-reference.md

@@ -504,7 +504,7 @@ Environment         |**Read-write.** The name of the Icinga environment. Include
 RunAsUser           |**Read-write.** Defines the user the Icinga 2 daemon is running as. Set in the Icinga 2 sysconfig.
 RunAsGroup          |**Read-write.** Defines the group the Icinga 2 daemon is running as. Set in the Icinga 2 sysconfig.
 MaxConcurrentChecks |**Read-write.** The number of max checks run simultaneously. Defaults to `512`.
-ApiBindHost         |**Read-write.** Overrides the default value for the ApiListener `bind_host` attribute. Defaults to `::`.
+ApiBindHost         |**Read-write.** Overrides the default value for the ApiListener `bind_host` attribute. Defaults to `::` if IPv6 is supported by the operating system and to `0.0.0.0` otherwise.
 ApiBindPort         |**Read-write.** Overrides the default value for the ApiListener `bind_port` attribute. Not set by default.
 
 #### Application Runtime Constants <a id="icinga-constants-application-runtime"></a>

lib/base/configuration.cpp

@@ -8,7 +8,20 @@ using namespace icinga;
 
 REGISTER_TYPE(Configuration);
 
-String Configuration::ApiBindHost{"::"};
+String Configuration::ApiBindHost = []() {
+#ifndef _WIN32
+	// Automatically fall back to an IPv4 default if socket() tells us that IPv6 is not supported.
+	int fd = socket(AF_INET6, SOCK_STREAM, 0);
+	if (fd < 0 && errno == EAFNOSUPPORT) {
+		return "0.0.0.0";
+	} else if (fd >= 0) {
+		close(fd);
+	}
+#endif /* _WIN32 */
+
+	return "::";
+}();
+
 String Configuration::ApiBindPort{"5665"};
 bool Configuration::AttachDebugger{false};
 String Configuration::CacheDir;