In Golang http client, what does Host mean in MaxConnsPerHost and MaxIdleConnsPerHost?-CodePudding

In MaxConnsPerHost and MaxIdleConnsPerHost in GO HTTP package, is "Host" a domain(i.e., yahoo.com) or an IP address? The actual meaning of "Host" will affect my settings for the connection pool.

CodePudding user response：

The host is the following part of a URL:

http://THIS.IS.THE.HOST/path/to/endpoint
       ^^^^^^^^^^^^^^^^

The underlined part of the URL is the host. The host can either be a domain name or an IP address - it depends on the URL you use. Note that it does not depend on the server answering the request.

For example, in the following:

http://127.0.0.1/api/list-all

The host is 127.0.0.1. But in the following:

http://example.com/api/list-all

The host is example.com.

If you have two servers configured like the following:

                     ┌───── HTTP Server 1 (10.20.30.40)
                     │        ├ www.foo.com (default)
                     │        └ www.bar.com
                     │
  DNS Load ──────────┤
  Balancer           │
                     └───── HTTP Server 2 (11.22.33.44)
                              └ www.bar.com (default)

Then http://www.bar.com is considered the same host even though it is served by two different IP addresses (10.20.30.40 and 11.22.33.44 - note: DNS load balancers do not handle HTTP request instead it handles DNS requests and will send different IP addresses to different clients to load-balance)

However 11.22.33.44 and www.bar.com are considered two different hosts even though both serve the exact same content.

Similarly www.foo.com and www.bar.com and 10.20.30.40 are considered 3 different hosts even though they are all served by the same server and same IP address (if the load balancer for www.bar.com resolve to 10.20.30.40).

CodePudding user response：

“Host” in http://www.example.com/abc/def is www.example.com.

The host may correspond to multiple IP addresses. This is normal.