Upstream: allow recovery from "429 Too Many Requests" response.

This change adds "http_429" parameter to "proxy_next_upstream" for
retrying rate-limited requests, and to "proxy_cache_use_stale" for
serving stale cached responses after being rate-limited.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

src/http/modules/ngx_http_fastcgi_module.c

@@ -211,6 +211,7 @@ static ngx_conf_bitmask_t  ngx_http_fastcgi_next_upstream_masks[] = {
     { ngx_string("http_503"), NGX_HTTP_UPSTREAM_FT_HTTP_503 },
     { ngx_string("http_403"), NGX_HTTP_UPSTREAM_FT_HTTP_403 },
     { ngx_string("http_404"), NGX_HTTP_UPSTREAM_FT_HTTP_404 },
+    { ngx_string("http_429"), NGX_HTTP_UPSTREAM_FT_HTTP_429 },
     { ngx_string("updating"), NGX_HTTP_UPSTREAM_FT_UPDATING },
     { ngx_string("off"), NGX_HTTP_UPSTREAM_FT_OFF },
     { ngx_null_string, 0 }

src/http/modules/ngx_http_proxy_module.c

@@ -220,6 +220,7 @@ static ngx_conf_bitmask_t  ngx_http_proxy_next_upstream_masks[] = {
     { ngx_string("http_504"), NGX_HTTP_UPSTREAM_FT_HTTP_504 },
     { ngx_string("http_403"), NGX_HTTP_UPSTREAM_FT_HTTP_403 },
     { ngx_string("http_404"), NGX_HTTP_UPSTREAM_FT_HTTP_404 },
+    { ngx_string("http_429"), NGX_HTTP_UPSTREAM_FT_HTTP_429 },
     { ngx_string("updating"), NGX_HTTP_UPSTREAM_FT_UPDATING },
     { ngx_string("off"), NGX_HTTP_UPSTREAM_FT_OFF },
     { ngx_null_string, 0 }

src/http/modules/ngx_http_scgi_module.c

@@ -82,6 +82,7 @@ static ngx_conf_bitmask_t ngx_http_scgi_next_upstream_masks[] = {
     { ngx_string("http_503"), NGX_HTTP_UPSTREAM_FT_HTTP_503 },
     { ngx_string("http_403"), NGX_HTTP_UPSTREAM_FT_HTTP_403 },
     { ngx_string("http_404"), NGX_HTTP_UPSTREAM_FT_HTTP_404 },
+    { ngx_string("http_429"), NGX_HTTP_UPSTREAM_FT_HTTP_429 },
     { ngx_string("updating"), NGX_HTTP_UPSTREAM_FT_UPDATING },
     { ngx_string("off"), NGX_HTTP_UPSTREAM_FT_OFF },
     { ngx_null_string, 0 }

src/http/modules/ngx_http_uwsgi_module.c

@@ -114,6 +114,7 @@ static ngx_conf_bitmask_t ngx_http_uwsgi_next_upstream_masks[] = {
     { ngx_string("http_503"), NGX_HTTP_UPSTREAM_FT_HTTP_503 },
     { ngx_string("http_403"), NGX_HTTP_UPSTREAM_FT_HTTP_403 },
     { ngx_string("http_404"), NGX_HTTP_UPSTREAM_FT_HTTP_404 },
+    { ngx_string("http_429"), NGX_HTTP_UPSTREAM_FT_HTTP_429 },
     { ngx_string("updating"), NGX_HTTP_UPSTREAM_FT_UPDATING },
     { ngx_string("off"), NGX_HTTP_UPSTREAM_FT_OFF },
     { ngx_null_string, 0 }

src/http/ngx_http_upstream.c

@@ -436,6 +436,7 @@ static ngx_http_upstream_next_t  ngx_http_upstream_next_errors[] = {
     { 504, NGX_HTTP_UPSTREAM_FT_HTTP_504 },
     { 403, NGX_HTTP_UPSTREAM_FT_HTTP_403 },
     { 404, NGX_HTTP_UPSTREAM_FT_HTTP_404 },
+    { 429, NGX_HTTP_UPSTREAM_FT_HTTP_429 },
     { 0, 0 }
 };
 
@@ -4126,6 +4127,10 @@ ngx_http_upstream_next(ngx_http_request_t *r, ngx_http_upstream_t *u,
         status = NGX_HTTP_NOT_FOUND;
         break;
 
+    case NGX_HTTP_UPSTREAM_FT_HTTP_429:
+        status = NGX_HTTP_TOO_MANY_REQUESTS;
+        break;
+
     /*
      * NGX_HTTP_UPSTREAM_FT_BUSY_LOCK and NGX_HTTP_UPSTREAM_FT_MAX_WAITING
      * never reach here

src/http/ngx_http_upstream.h

@@ -26,10 +26,11 @@
 #define NGX_HTTP_UPSTREAM_FT_HTTP_504        0x00000080
 #define NGX_HTTP_UPSTREAM_FT_HTTP_403        0x00000100
 #define NGX_HTTP_UPSTREAM_FT_HTTP_404        0x00000200
-#define NGX_HTTP_UPSTREAM_FT_UPDATING        0x00000400
-#define NGX_HTTP_UPSTREAM_FT_BUSY_LOCK       0x00000800
-#define NGX_HTTP_UPSTREAM_FT_MAX_WAITING     0x00001000
-#define NGX_HTTP_UPSTREAM_FT_NON_IDEMPOTENT  0x00002000
+#define NGX_HTTP_UPSTREAM_FT_HTTP_429        0x00000400
+#define NGX_HTTP_UPSTREAM_FT_UPDATING        0x00000800
+#define NGX_HTTP_UPSTREAM_FT_BUSY_LOCK       0x00001000
+#define NGX_HTTP_UPSTREAM_FT_MAX_WAITING     0x00002000
+#define NGX_HTTP_UPSTREAM_FT_NON_IDEMPOTENT  0x00004000
 #define NGX_HTTP_UPSTREAM_FT_NOLIVE          0x40000000
 #define NGX_HTTP_UPSTREAM_FT_OFF             0x80000000
 
@@ -38,7 +39,8 @@
                                              |NGX_HTTP_UPSTREAM_FT_HTTP_503  \
                                              |NGX_HTTP_UPSTREAM_FT_HTTP_504  \
                                              |NGX_HTTP_UPSTREAM_FT_HTTP_403  \
-                                             |NGX_HTTP_UPSTREAM_FT_HTTP_404)
+                                             |NGX_HTTP_UPSTREAM_FT_HTTP_404  \
+                                             |NGX_HTTP_UPSTREAM_FT_HTTP_429)
 
 #define NGX_HTTP_UPSTREAM_INVALID_HEADER     40