Web
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nginx — web server and reverse proxy
nginx serves sites from disk and forwards requests to applications; it picks a site by Host, nginx -t checks the config.
13 minnginx -tsystemctl reloadnginx -T -
HTTP — requests, responses, status codes and headers
HTTP is the web protocol: a client sends a method, path and headers; the server replies with a code, headers, body.
11 mincurl -icurl -Icurl -v -
curl — HTTP requests from the console
curl sends HTTP and HTTPS requests from the console: status code, headers, the whole exchange, certificate checks.
7 mincurl -icurl -Icurl -v -
TLS and certificates — openssl, the chain, verification
A TLS certificate binds a server key to a site name; openssl reads its fields, checks the chain and issues a new one.
11 minopensslopenssl verifycurl --cacert -
HAProxy — load balancer
Load balancing and proxying TCP/HTTP — backends, health checks, statistics.
4 minhaproxy -csystemctl reloadecho