Differences between HTTP and HTTPS

HTTP vs HTTPS at a glance

Hypertext Transfer Protocol (HTTP) is a protocol used when your web browser (client), requests information from a server.

• URL begins with "http://"
• uses port 80 for communication
• it is unsecured
• no encryption is in place
• no certificates are required.

Hypertext Transfer Protocol Secure (HTTPS) is combination of Hypertext Transfer Protocol (HTTPS) and Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols.

• URL begins with "https://"
• uses port 443 for communication
• is a more secure way to sending data from a client to a server and way back
• communication is encrypted
• encryption SSL certificates are required

Why the protocol matters when load testing

The scheme in your target URL, http:// versus https://, is not cosmetic. It tells the load test agent which protocol to speak and which port to connect on by default, 80 for HTTP and 443 for HTTPS. Testing http://example.com and https://example.com are two different requests, potentially handled by two different server configurations, so make sure the URL you enter matches the one your real users actually hit.

TLS handshake overhead

HTTPS adds a TLS handshake before any application data is exchanged: the client and server negotiate a cipher, exchange and validate certificates, and agree on session keys. That negotiation costs extra round trips and CPU time compared to plain HTTP, especially on the first connection. Two things reduce that cost in practice:

• Connection reuse (keep-alive): once a TLS connection is established, subsequent requests over the same connection skip the handshake, so most of the overhead is a one-time cost per connection, not per request.
• Session resumption: modern TLS lets a client resume a previous session without a full handshake, cutting the cost further on repeat connections.

At high concurrency, when many virtual users open many new connections at once, TLS handshakes become CPU-intensive on the server side. If you're comparing HTTP and HTTPS performance for the same endpoint, expect HTTPS to look slightly slower on connection-heavy tests, and do not mistake that difference for an application-level regression.

Certificate validation

Because HTTPS requires a valid certificate, a load test agent connecting to your endpoint needs to be able to validate it. A certificate that is expired, self-signed, or issued by a private or internal certificate authority can cause connection failures that have nothing to do with your application's actual performance. If you see connection errors only on the HTTPS variant of an endpoint, check the certificate chain before assuming it is a load or capacity problem.

Redirects between HTTP and HTTPS

Many sites redirect all HTTP traffic to HTTPS with a 301 or 302 response. If you point a load test at the HTTP URL expecting it to reach your application directly, you are actually measuring the redirect hop plus the follow-up HTTPS request, which adds latency that would not exist if you tested the HTTPS endpoint directly. For accurate baseline numbers, test the final HTTPS URL your users land on. Only test the HTTP URL directly if you specifically want to measure the redirect behavior itself.

For what counts as a valid target URL, including the http or https prefix, see https://loadfocus.com/docs/knowledge-base/using-valid-url-endpoints.