System.CalloutException: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 503 Service Unavailable"

Question

I'm trying to make an HTTP Request to other System.

They provided the endpoint URL which contains a Port number.

https://Test.com:50001/RESTAP/BGN/PRDV/CREATE

When I'm trying to make the request I facing with this ERROR:

System.CalloutException: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 503 Service Unavailable"

although I have added the URL in remote sites.

I saw some solutions about this Error (Mostly on a similar error : with "HTTP/1.0 404 Not Found") - like - ask the Other system to whiteList Salesforce IPs.

1. There are many IPs to add to the WhiteList by the other System From here: https://help.salesforce.com/articleView?id=000321501&type=1&mode=1.

This is the best practice to add to White List by IP? If it will change (Delete, Add, Update) SF will notify me about that? Can I send them URL Instead?

2. How can I send the Port using Apex? this is my code :

           Http httpProtocol = new Http();
           HttpRequest request = new HttpRequest();
           String url = 'https://Test.com/RESTAP/BGN/PRDV/CREATE';
           String username2 = 'Name';
           String password2 = 'Passowrd';
           Blob headerValue = Blob.valueOf(username2 + ':' + password2);
           String authorizationHeader = 'BASIC ' + EncodingUtil.base64Encode(headerValue);
           request.setEndpoint(url);
           request.setMethod('POST');
           request.setHeader('Authorization', authorizationHeader);
           request.setTimeout(60000);
   
   
           request.setHeader('Content-Type','application/json');
           request.setHeader('proxyPort','50001');
           request.setHeader('proxyHost','PROXYHOST URL');
           request.setHeader('proxySet','true');
   
           HttpResponse response = httpProtocol.send(request);
   

I tried to send the port via HEADER like above and via change the URL to :

String URL = 'https://Test.com:50001/RESTAP/BGN/PRDV/CREATE'; 

But the error keeps coming.

Is there another thing I need to consider except ask the other System to add SF to the whiteList?

Thanks!

Answer 1

https://Test.com:50001/RESTAP/BGN/PRDV/CREATE

This URL looks like the one accessible only within company's network.

Ideally, your integration endpoint should be something which is accessible over internet since Salesforce integration calls are over internet.