I am newbie to Nginx and I am using Nginx with PostgreSQL database.
When there is a http request to the server I want to extract one of the
input variables in the request,
query the Database and retrun the result, the variable inside the
postgres_query is empty.
But when I try to print the value of “$1” variable and also after
assigning
it to the variable “$tenantID” I do get the value.
I guess in the eval block the postgres_escape is not getting set.
Can some one throw some light on this issue if I am doing something
wrong.
Also is there any supporting module to use the echo statements inside
the
postgres block.
location ~ ^/tenantservices/(.)/(.)/(.)/(.)
{
echo teh complete request uri is :$request_uri;
echo The first parameter is :$1;
echo the second aprameter is :$2;
echo the third parameter is :$3;
echo the fourth param is :$4;
set $tenantID $1;
set $serviceName $2;
set $userID $3;
set $endPointName $4;
{
default_type ‘text/plain’;
postgres_pass tenantdatabase;
postgres_escape $tenantURID $tenantID;
postgres_query “SELECT max_no_clusters FROM load_balancer
WHERE
id=$tenantURID”;
postgres_output value ;
}
echo MaxNoOfclusters is : $max_no_clusters;
}
Log message on Nginx:
2014/03/04 15:46:05 [error] 31995#0: *152 postgres: “postgres_output
value”
received 0 value(s) instead of expected single value in location
“/eval_155080700” while processing result from PostgreSQL database,
But when I try to print the value of “$1” variable and also after assigning
it to the variable “$tenantID” I do get the value.
I guess in the eval block the postgres_escape is not getting set.
The “eval” directive always runs before the directives of the standard
ngx_rewrite module. No matter in what order you write them down in
nginx.conf.
As a co-maintainer of ngx_postgres, I recommend you use ngx_lua module
to communicate with ngx_postgres.
Basically you can use rewrite_by_lua to inject some Lua code and use
ngx.location.capture to issue a subrequest to your postgres location.
I have used ngx.location.capture for extracting the values from postgres
database as suggested by you.
I had to make a series of postgres calls so I used content_by_lua along
by
sharing the varialbes as I had to query tables from multiple databases.
I have now got the needed nodeIP and port ultimately. But I am not able
to
redirect the url.
I have used rewrite_by_lua in the end to redirect to the new url, but it
does not seem to be happening.
If I use http rewrite module again the values of the nodeIP and port
would
be empty.
Could you please suggest how to redirect to the new url with the
extracted
nodeIP and port?
Thanks in advance,
Arun
CODE:
location /postgresrewrite
{
rewrite ^ "http://$nodeIP:$port/$inputURI";
}
location ~ ^/tenantservices/(.)/(.)/(.)/(.)
{
set $inputURI $request_uri;
set $tenantURI $1;
set $serviceName $2;
set $userID $3;
set $endPointName $4;
Also, it is a bad idea to enable “share_all_vars” due to potential bad
side-effects that lead to weird issues that are extremely hard to
debug. Just share the NGINX variables you want to share.
I had to make a series of postgres calls so I used content_by_lua along by
sharing the varialbes as I had to query tables from multiple databases.
No, you should use rewrite_by_lua exclusively for all the
ngx.location.capture calls here I think.
I have now got the needed nodeIP and port ultimately. But I am not able to
redirect the url.
I have used rewrite_by_lua in the end to redirect to the new url, but it
does not seem to be happening.
rewrite_by_lua always runs before content_by_lua. Because NGINX’s
“rewrite” phase always runs before the “content” phase.
Just put all your subrequest calls in the same code chunk as your
redirect Lua code in rewrite_by_lua.
What kind of redirect do you really need? 301? 302? or internal
redirect? See
BTW, you’re recommended to join the openresty-en mailing list and
discuss such things there: https://groups.google.com/group/openresty-en You might get faster and
more responses on that list.
The use case I am trying to test is the client sends a request to nginx
server with some parameters say “/a/b/c/d”: http://NginxHost/a/b/c/d
Depending on the parameters a,b,c and d I will get the IP and port of
the
destination server (by communicating with postgres) where the request
must
be redirected to ie the new url is of the form: http://IP:port/a/b/c/d.
Using both ngx.redirect and nginx.exec() are giving errors.
I tried to redirect the url to “www.google.com” using ngx.redirect
inside
rewrite_by_lua. Even I get the same error.
You had mentioned that " redirects in a subrequest won’t affect its
parent
requests." Does that mean that I cannot change the url inside the
rewrite_by_lua module?
I cannot use http rewrite module as this will be executed before the
rewrite_by_lua code is executed.
Please suggest what can be done to redirect the parent url to new url.
Thank you,
Arun
ERROR LOG:
CODE:
location /postgresrewrite
{
rewrite ^ “http://www.google.co.in”;
}
ngx.exec(“/postgresrewrite”);
LOG:
2014/03/05 22:59:42 [error] 8129#0: *374 lua entry thread aborted:
runtime
error: [string “rewrite_by_lua”]:32: attempt to call ngx.exec after
sending
out response headers
stack traceback:
coroutine 0:
[C]: in function ‘exec’
[string “rewrite_by_lua”]:32: in function <[string
“rewrite_by_lua”]:1> while sending to client, client: xx.xx.xx.xx,
server:
localhost, request: “GET
/tenantservices/ArunTenant.com/Service1/13717e3b-c32d-4172-a316-74857b1237e1/httpSoapProvider
HTTP/1.1”, host: “yy.yy.yy.yy”
CODE:
return ngx.redirect(“http://www.google.co.in”);
LOG:
2014/03/05 22:23:05 [error] 5397#0: *366 lua entry thread aborted:
runtime
error: [string “rewrite_by_lua”]:32: attempt to call ngx.redirect after
sending out the headers
stack traceback:
coroutine 0:
[C]: in function ‘redirect’
[string “rewrite_by_lua”]:32: in function <[string
“rewrite_by_lua”]:1> while sending to client, client: xx.xx.xx.xx,
server:
localhost, request: “GET
/tenantservices/ArunTenant.com/Service1/13717e3b-c32d-4172-a316-74857b1237e1/httpSoapProvider
HTTP/1.1”, host: “yy.yy.yy.yy”
Depending on the parameters a,b,c and d I will get the IP and port of the
destination server (by communicating with postgres) where the request must
be redirected to ie the new url is of the form: http://IP:port/a/b/c/d.
You need either a 301/302 redirect or a proxy_pass to go to external
target.
Below is an example:
rewrite_by_lua '
local new_target = "http:/IP:port/a/b/c/d"
return ngx.redirect(new_target)
';
Using both ngx.redirect and nginx.exec() are giving errors.
I tried to redirect the url to “www.google.com” using ngx.redirect inside
rewrite_by_lua. Even I get the same error.
Please provide a minimal but still complete example that can reproduce
the issue.
You had mentioned that " redirects in a subrequest won’t affect its parent
requests." Does that mean that I cannot change the url inside the
rewrite_by_lua module?
You created a subrequest with ngx.location.capture and you used the
“rewrite” directive in the location targeted by the subrequest in the
hope that it will change the parent request calling
ngx.location.capture.
What you need is to initiate redirects in your main request. So you
should not use ngx.location.capture for a redirect. I never say you
cannot perform redirect in rewrite_by_lua. Do not get me wrong.
I cannot use http rewrite module as this will be executed before the
rewrite_by_lua code is executed.
No, as I’ve said, you should use the Lua API in rewrite_by_lua to
perform redirects.
2014/03/05 22:59:42 [error] 8129#0: *374 lua entry thread aborted: runtime
error: [string “rewrite_by_lua”]:32: attempt to call ngx.exec after sending
out response headers
The error clearly indicates the problem. You should not send the
response header before doing redirects (note that, ngx.say, ngx.print,
ngx.flush all trigger sending out the response header automatically,
so avoid them).
Regards,
-agentzh
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