DNS Caching Issue For community version

Server NGINX
1

Troubled up in DNS caching of the IP address for a given DNS name.

Adding the solution given below does not solve the problem of DNS
caching in
NGINX.

resolver 8.8.8.8;
set $upstream_endpoint https://example.net:8080;
location / {
proxy_pass $upstream_endpoint;
}

Is there any solutions?

Posted at Nginx Forum:

2

From Manual:

By default, nginx caches answers using the TTL value of a response. An
optional|valid|parameter allows overriding it:

resolver 127.0.0.1 [::1]:5353 valid=30s;

Before version 1.1.9, tuning of caching time was not possible, and
nginx always cached answers for the duration of 5 minutes.

Best regards,
Vintila Mihai Alexandru

3

Even adding the valid parameter the issue was not solved.

Posted at Nginx Forum:

4

I wanted check whether the resolver solves the DNS in a dynamic manner
when
the ip addresses changes.

So I add the given code after several findings and yet the resolving the
ip
address is not happening.

server{
…

resolver 8.8.8.8 valid=30s;
resolver_timeout 10s;
set $upstream “example.net”;

location / {
rewrite ^/(.*) /$1 break;
proxy_pass https://:3000$upstream;

    }

}

Posted at Nginx Forum:

5

Have you also checked that the DNS returns the correct value? As the
valid option means that nginx will ask the DNS server again, but if the
DNS replies with same old ip… Also you might check using directly the
hostname as it might be possible that there is a bug when using
variables.

Best regards,
Vintila Mihai Alexandru

6

Even adding the valid parameter the issue was not solved.

And what is the issue actually? Just saying “DNS caching issue”
and “problem” isn’t really helpful.

7

Hello!

On Thu, May 12, 2016 at 06:11:36AM -0400, RT.Nat wrote:

resolver_timeout 10s;
set $upstream “example.net”;

location / {
rewrite ^/(.*) /$1 break;
proxy_pass https://:3000$upstream;

    }

}

Note if you have upstream “example.net” defined elsewhere, nginx
will use it, and dynamic DNS resolution will not be used. Note
well that upstream may be defined either explicitly, using

upstream example.net {
    ...
}

or implicitly, using a proxy_pass to the given name:

proxy_pass http://example.net;

The latter sometimes confuses people trying to use proxy_pass with
variables to trigger dynamic DNS resolution of upstream names.

–
Maxim D.
http://nginx.org/

8

Not clear regarding, " Also you might check using directly the hostname
as
it might be possible that there is a bug when using variables."

I tried adding the variable for resolving the dns but still the ip
address
does not changes. Is there any other way? or is there any bug in my
script.

resolver 8.8.8.8 valid=30s;
resolver_timeout 10s;
set $checkup “example.net”;

location / {
rewrite ^/(.*) /$1 break;
proxy_pass https://:8080$checkup;
}

even adding the following codes instead of the above proxy pass doesnt
work.

proxy_pass https://example.net:8080$request_uri;
proxy_pass https://example.net:8080;

Posted at Nginx Forum:

9

I cannot install the above module.

/Downloads/nginx-upstream-dynamic-servers-master$ make install
make: *** No rule to make target `install’. Stop.

May i know is there any problem in my machine( any required
prerequistes).

Posted at Nginx Forum:

10

Maybe You should try this module:

Regards,
Biazus

On Fri, May 13, 2016 at 3:13 AM, RT.Nat [email protected]
wrote:

location / {
Posted at Nginx Forum:
Re: DNS Caching Issue For community version

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11

On Fri, May 13, 2016 at 02:13:05AM -0400, RT.Nat wrote:

Hi there,

why do you think that this does not work?

As in: what request do you make that give you an unexpected response?
And
can you also show the “dig” command that shows that the nominated dns
server has changed the resolution address that it provides?

I tried adding the variable for resolving the dns but still the ip address
does not changes. Is there any other way? or is there any bug in my script.

When I use:

==
http {
server {
listen 8080;
resolver 8.8.8.8 valid=20s;
set $up “www.example.net”;
location / {
proxy_pass http://$up;
}
}
}

I can do:

date; while :; do curl http://127.0.0.1:8080/; sleep 3; done

and I can also do

tcpdump -nn port 53

and the first command shows the remote web server content every few
seconds, while the second command show that a new dns request is made
more than 20 seconds after the previous one:

===
21:31:00.572450 IP 192.168.224.128.52862 > 8.8.8.8.53: 12516+ A?
www.example.net. (33)
21:31:00.631578 IP 8.8.8.8.53 > 192.168.224.128.52862: 12516 1/0/0 A
93.184.216.34 (49)
21:31:23.829429 IP 192.168.224.128.52862 > 8.8.8.8.53: 5096+ A?
www.example.net. (33)
21:31:23.873474 IP 8.8.8.8.53 > 192.168.224.128.52862: 5096 1/0/0 A
93.184.216.34 (49)
21:31:47.135984 IP 192.168.224.128.52862 > 8.8.8.8.53: 37996+ A?
www.example.net. (33)
21:31:47.165754 IP 8.8.8.8.53 > 192.168.224.128.52862: 37996 1/0/0 A
93.184.216.34 (49)

Now, I don’t control the google name server, and I can’t make
www.example.net get an updated address at will; but the above does seem
to show that the nginx resolver is making a fresh dns request when it
is supposed to.

Do you see something else in your test?

f

Francis D. [email protected]

12

You have to configure your nginx to use it like any other module.
For instance,
cd /Downloads/nginx
./configure
–add-module=/Downloads/nginx-upstream-dynamic-servers-master
make
make install