upstream retries with a single server

[Arvind Jayaprakash]

On Nov 21, Maxim Dounin wrote:
>Hello!
>
>On Sat, Nov 20, 2010 at 09:48:15PM +0530, Arvind Jayaprakash wrote:
>
>> Hello,
>>   From the way I understand if there are 'n' servers listed as part of
>> an upstream block & upstream returns failure (as defined by
>> proxy_next_upstream), then nginx retries the same request on another
>> upstream server and this repeats till every upstream is tried once
>> (excluding those that are considered to be down).
>
>Yes.
>
>> If an upstream block is defined with exactly one active server, I see
>> that the request gets retried on the same upstream in case of a failure
>> upto 'max_retries' number of times. Logically, I'd expect it to try just
>> once and then give up if upstream fails to provide a suitable response.
>
>There is no such thing as 'max_retries'.  As in previous case, all 
>(i.e. the only one in this case) upstreams are tried once and then 
>appropriate error returned.

My bad, I meant max_fails.


I've managed to reproduce a problem where the same upstream gets
retried.

When an upstream block contains one active and one backup server, the
same request gets retried. Commenting out the backup (line 22 in the
conf) however seems to exhibit the defined behaviour of try exactly
once. The access log contains the status for the 2 cases.

I've been able to reproduce this on many versions (0.8.[33,34,53])
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127.0.0.1 - - [21/Nov/2010:18:35:30 +0530] "GET /err.php HTTP/1.1" UP:(502) (0.000) (127.0.0.1:80)502 383 "-" "lwp-request/5.827 libwww-perl/5.831" "-"
127.0.0.1 - - [21/Nov/2010:18:35:35 +0530] "GET /err.php HTTP/1.1" UP:(502, 502, 502, 502, 502, 502) (0.000, 0.000, 0.000, 0.000, 0.000, 0.000) (127.0.0.1:80, 127.0.0.1:80, 127.0.0.1:80, 127.0.0.1:80, 127.0.0.1:80, 127.0.0.1:801)502 383 "-" "lwp-request/5.827 libwww-perl/5.831" "-"
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#user  nobody;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
error_log  logs/error.log  debug;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


http {

	upstream ussss
	{
		server 127.0.0.1:80 max_fails=5;
		server 127.0.0.1:801 max_fails=5 backup;
	}

	upstream w2
	{
		server 127.0.0.1:80 weight=1 max_fails=2 fail_timeout=60;
		server 127.0.0.1:801 weight=100 max_fails=2 fail_timeout=60;
	}

    include       mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      'UP:($upstream_status) ($upstream_response_time) ($upstream_addr)'
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  logs/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    #gzip  on;

    server {
        listen       8081;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        location / {
			proxy_pass http://ussss;
			proxy_connect_timeout 2;
			proxy_read_timeout 2;
        }

		location /autodocs {
			proxy_pass http://w2;
		}

        #error_page  404              /404.html;

        # redirect server error pages to the static page /50x.html
        #
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }

        # proxy the PHP scripts to Apache listening on 127.0.0.1:80
        #
        #location ~ \.php$ {
        #    proxy_pass   http://127.0.0.1;
        #}

        # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
        #
        #location ~ \.php$ {
        #    root           html;
        #    fastcgi_pass   127.0.0.1:9000;
        #    fastcgi_index  index.php;
        #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
        #    include        fastcgi_params;
        #}

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #
        #location ~ /\.ht {
        #    deny  all;
        #}
		location /wireframes {
			proxy_pass http://localhost:8000;
		}

		location /advertiser {
			proxy_pass http://localhost:8000;
		}

		location ~ /adv(css|js|images)
		{
			root /home/arvindj/src/people/anomalizer/dj-m3/inmobi_ui/media-ui;
		}
    }


    # another virtual host using mix of IP-, name-, and port-based configuration
    #
    #server {
    #    listen       8000;
    #    listen       somename:8080;
    #    server_name  somename  alias  another.alias;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}


    # HTTPS server
    #
    #server {
    #    listen       443;
    #    server_name  localhost;

    #    ssl                  on;
    #    ssl_certificate      cert.pem;
    #    ssl_certificate_key  cert.key;

    #    ssl_session_timeout  5m;

    #    ssl_protocols  SSLv2 SSLv3 TLSv1;
    #    ssl_ciphers  ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP;
    #    ssl_prefer_server_ciphers   on;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}

}