Suddenly Proxy stop answering to Users TCP/MISS 503 error

Error : Users are experiencing web site surfing issues with the proxy. They can not surf any website and in the access.log file all the requests have logged as TCP/MISS 503 error message.

To rectify the issue try with the below workarounds.

1. Clear the squid cache folder located in /var/spool/squid
2. Rearrange the ACLs with new configuration.

But issue remains. Then I have given full access to all the users to confirm the issue. Once users get the full access they able to access the Internet. With that it's confirmed that issue is with the proxy.

While monitoring the access.log it found that users were able to access the sites with the IP address. Then able to figure out the root cause is that proxy failed to resolve Hostname to IP address.

Solution :

checked the squid configuration file. /etc/squid/squid.conf

It has three name servers configured.

I have changed the name servers to google DNS, then restart the proxy server. Finally it fixed and users able to surf Internet through proxy.