docs/en/latest/debug-function.md - apisix - Git at Google

 ---
 title: Debug Function
 ---

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 ## `5xx` response status code

 Similar `5xx` status codes such as 500, 502, 503, etc., are the status codes in response to a server error. When a request has a `5xx` status code; it may come from `APISIX` or `Upstream`. How to identify the source of these response status codes is a very meaningful thing. It can quickly help us determine the problem. (When modifying the configuration `show_upstream_status_in_response_header` in `conf/config.yaml` to `true`, all upstream status codes will be returned, not only `5xx` status.)

 ## How to identify the source of the `5xx` response status code

 In the response header of the request, through the response header of `X-APISIX-Upstream-Status`, we can effectively identify the source of the `5xx` status code. When the `5xx` status code comes from `Upstream`, the response header `X-APISIX-Upstream-Status` can be seen in the response header, and the value of this response header is the response status code. When the `5xx` status code is derived from `APISIX`, there is no response header information of `X-APISIX-Upstream-Status` in the response header. That is, only when the status code of `5xx` is derived from Upstream will the `X-APISIX-Upstream-Status` response header appear.

 ## Example

 >Example 1: `502` response status code comes from `Upstream` (IP address is not available)

 ```shell
 $ curl http://127.0.0.1:9180/apisix/admin/routes/1  -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
 {
     "methods": ["GET"],
     "upstream": {
         "nodes": {
             "127.0.0.1:1": 1
         },
         "type": "roundrobin"
     },
     "uri": "/hello"
 }'
 ```

 Test:

 ```shell
 $ curl http://127.0.0.1:9080/hello -v
 ......
 < HTTP/1.1 502 Bad Gateway
 < Date: Wed, 25 Nov 2020 14:40:22 GMT
 < Content-Type: text/html; charset=utf-8
 < Content-Length: 154
 < Connection: keep-alive
 < Server: APISIX/2.0
 < X-APISIX-Upstream-Status: 502
 <
 <html>
 <head><title>502 Bad Gateway</title></head>
 <body>
 <center><h1>502 Bad Gateway</h1></center>
 <hr><center>openresty</center>
 </body>
 </html>

 ```

 It has a response header of `X-APISIX-Upstream-Status: 502`.

 >Example 2: `502` response status code comes from `APISIX`

 ```shell
 $ curl http://127.0.0.1:9180/apisix/admin/routes/1  -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
 {
     "plugins": {
         "fault-injection": {
             "abort": {
                 "http_status": 500,
                 "body": "Fault Injection!\n"
             }
         }
     },
     "uri": "/hello"
 }'
 ```

 Test：

 ```shell
 $ curl http://127.0.0.1:9080/hello -v
 ......
 < HTTP/1.1 500 Internal Server Error
 < Date: Wed, 25 Nov 2020 14:50:20 GMT
 < Content-Type: text/plain; charset=utf-8
 < Transfer-Encoding: chunked
 < Connection: keep-alive
 < Server: APISIX/2.0
 <
 Fault Injection!
 ```

 There is no response header for `X-APISIX-Upstream-Status`.

 >Example 3: `Upstream` has multiple nodes, and all nodes are unavailable

 ```shell
 $ curl http://127.0.0.1:9180/apisix/admin/upstreams/1  -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
 {
     "nodes": {
         "127.0.0.3:1": 1,
         "127.0.0.2:1": 1,
         "127.0.0.1:1": 1
     },
     "retries": 2,
     "type": "roundrobin"
 }'
 ```

 ```shell
 $ curl http://127.0.0.1:9180/apisix/admin/routes/1  -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
 {
     "uri": "/hello",
     "upstream_id": "1"
 }'
 ```

 Test：

 ```shell
 $ curl http://127.0.0.1:9080/hello -v
 < HTTP/1.1 502 Bad Gateway
 < Date: Wed, 25 Nov 2020 15:07:34 GMT
 < Content-Type: text/html; charset=utf-8
 < Content-Length: 154
 < Connection: keep-alive
 < Server: APISIX/2.0
 < X-APISIX-Upstream-Status: 502, 502, 502
 <
 <html>
 <head><title>502 Bad Gateway</title></head>
 <body>
 <center><h1>502 Bad Gateway</h1></center>
 <hr><center>openresty</center>
 </body>
 </html>
 ```

 It has a response header of `X-APISIX-Upstream-Status: 502, 502, 502`.
	---
	title: Debug Function
	---

	<!--
	#
	# Licensed to the Apache Software Foundation (ASF) under one or more
	# contributor license agreements. See the NOTICE file distributed with
	# this work for additional information regarding copyright ownership.
	# The ASF licenses this file to You under the Apache License, Version 2.0
	# (the "License"); you may not use this file except in compliance with
	# the License. You may obtain a copy of the License at
	#
	# http://www.apache.org/licenses/LICENSE-2.0
	#
	# Unless required by applicable law or agreed to in writing, software
	# distributed under the License is distributed on an "AS IS" BASIS,
	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	# See the License for the specific language governing permissions and
	# limitations under the License.
	#
	-->

	## `5xx` response status code

	Similar `5xx` status codes such as 500, 502, 503, etc., are the status codes in response to a server error. When a request has a `5xx` status code; it may come from `APISIX` or `Upstream`. How to identify the source of these response status codes is a very meaningful thing. It can quickly help us determine the problem. (When modifying the configuration `show_upstream_status_in_response_header` in `conf/config.yaml` to `true`, all upstream status codes will be returned, not only `5xx` status.)

	## How to identify the source of the `5xx` response status code

	In the response header of the request, through the response header of `X-APISIX-Upstream-Status`, we can effectively identify the source of the `5xx` status code. When the `5xx` status code comes from `Upstream`, the response header `X-APISIX-Upstream-Status` can be seen in the response header, and the value of this response header is the response status code. When the `5xx` status code is derived from `APISIX`, there is no response header information of `X-APISIX-Upstream-Status` in the response header. That is, only when the status code of `5xx` is derived from Upstream will the `X-APISIX-Upstream-Status` response header appear.

	## Example

	>Example 1: `502` response status code comes from `Upstream` (IP address is not available)

	```shell
	$ curl http://127.0.0.1:9180/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
	{
	"methods": ["GET"],
	"upstream": {
	"nodes": {
	"127.0.0.1:1": 1
	},
	"type": "roundrobin"
	},
	"uri": "/hello"
	}'
	```

	Test:

	```shell
	$ curl http://127.0.0.1:9080/hello -v
	......
	< HTTP/1.1 502 Bad Gateway
	< Date: Wed, 25 Nov 2020 14:40:22 GMT
	< Content-Type: text/html; charset=utf-8
	< Content-Length: 154
	< Connection: keep-alive
	< Server: APISIX/2.0
	< X-APISIX-Upstream-Status: 502
	<
	<html>
	<head><title>502 Bad Gateway</title></head>
	<body>
	<center><h1>502 Bad Gateway</h1></center>
	<hr><center>openresty</center>
	</body>
	</html>

	```

	It has a response header of `X-APISIX-Upstream-Status: 502`.

	>Example 2: `502` response status code comes from `APISIX`

	```shell
	$ curl http://127.0.0.1:9180/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
	{
	"plugins": {
	"fault-injection": {
	"abort": {
	"http_status": 500,
	"body": "Fault Injection!\n"
	}
	}
	},
	"uri": "/hello"
	}'
	```

	Test：

	```shell
	$ curl http://127.0.0.1:9080/hello -v
	......
	< HTTP/1.1 500 Internal Server Error
	< Date: Wed, 25 Nov 2020 14:50:20 GMT
	< Content-Type: text/plain; charset=utf-8
	< Transfer-Encoding: chunked
	< Connection: keep-alive
	< Server: APISIX/2.0
	<
	Fault Injection!
	```

	There is no response header for `X-APISIX-Upstream-Status`.

	>Example 3: `Upstream` has multiple nodes, and all nodes are unavailable

	```shell
	$ curl http://127.0.0.1:9180/apisix/admin/upstreams/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
	{
	"nodes": {
	"127.0.0.3:1": 1,
	"127.0.0.2:1": 1,
	"127.0.0.1:1": 1
	},
	"retries": 2,
	"type": "roundrobin"
	}'
	```

	```shell
	$ curl http://127.0.0.1:9180/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
	{
	"uri": "/hello",
	"upstream_id": "1"
	}'
	```

	Test：

	```shell
	$ curl http://127.0.0.1:9080/hello -v
	< HTTP/1.1 502 Bad Gateway
	< Date: Wed, 25 Nov 2020 15:07:34 GMT
	< Content-Type: text/html; charset=utf-8
	< Content-Length: 154
	< Connection: keep-alive
	< Server: APISIX/2.0
	< X-APISIX-Upstream-Status: 502, 502, 502
	<
	<html>
	<head><title>502 Bad Gateway</title></head>
	<body>
	<center><h1>502 Bad Gateway</h1></center>
	<hr><center>openresty</center>
	</body>
	</html>
	```

	It has a response header of `X-APISIX-Upstream-Status: 502, 502, 502`.