Initial check in, forked from tengine module

https://github.com/alibaba/tengine/blob/master/src/http/modules/ngx_http_upstream_dynamic_module.c

Author: gfrankliu

CHANGES

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+* Initial check in, forked from https://github.com/alibaba/tengine

LICENSE

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+/* 
+ * Copyright (C) 2002-2013 Igor Sysoev
+ * Copyright (C) 2011,2013 Nginx, Inc.
+ * Copyright (C) 2010-2015 Alibaba Group Holding Limited
+ * Copyright (C) 2011-2013 Xiaozhe "chaoslawful" Wang
+ * Copyright (C) 2011-2013 Zhang "agentzh" Yichun
+ * Copyright (C) 2011-2013 Weibin Yao
+ * Copyright (C) 2012-2013 Sogou, Inc.
+ * Copyright (C) 2012-2013 NetEase, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */

README

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+Name
+ ngx_http_upstream_dynamic_module
+ This module provides the functionality to resolve domain names into IP addresses in an upstream at run-time. 
+ It comes from Taobao Tengine @ http://tengine.taobao.org
+
+Synopsis
+
+    upstream backend {
+        dynamic_resolve fallback=stale fail_timeout=30s;
+
+        server a.com;
+        server b.com;
+    }
+
+    server {
+        ...
+
+        location / {
+            proxy_pass http://backend;
+        }
+    }
+
+Notes
+
+ It is a tengine module from
+ https://github.com/alibaba/tengine/blob/master/src/http/modules/ngx_http_upstream_dynamic_module.c
+ and made to work with nginx 1.9
+ It follows original tengine license.

ngx_http_upstream_dynamic.md

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+Name
+====
+
+* ngx_http_upstream_dynamic_module
+
+Description
+===========
+
+* This module provides the functionality to resolve domain names into IP addresses in an upstream at run-time.
+
+Examples
+========
+
+    upstream backend {
+        dynamic_resolve fallback=stale fail_timeout=30s;
+
+        server a.com;
+        server b.com;
+    }
+
+    server {
+        ...
+
+        proxy_pass http://backend;
+    }
+
+Directives
+==========
+
+dynamic_resolve
+---------------
+
+**Syntax**: *dynamic_resolve [fallback=stale|next|shutdown] [fail_timeout=time]*
+
+**Default**: *-*
+
+**Context**: *upstream*
+
+Enable dynamic DNS resolving functionality in an upstream.
+
+The 'fallback' parameter specifies what action to take if a domain name can not be resolved into an IP address:
+
+* stale, use the original IP addresses resolved when tengine starts.
+* next, go to next availiable server in the upstream.
+* shutdown, finalize current request.
+
+The 'fail_timeout' parameter specifies how long time tengine considers the DNS server as unavailiable if a DNS query fails for a server in the upstream. In this period of time, all requests comming will follow what 'fallback' specifies.