Varnish
Default in varnish 5.2.1 keepalive is enabled, and set with a timeout of timeout_idle=5 seconds. which means that if no traffic goes through the tcp pipe in 5 seconds the TCP connection is closed.
If you are running HLS with a chunksize of 8 seconds you want to change timeout_idle to 8 seconds. you can change timeout_idle in a default installation by adding the following to /etc/varnish/varnish.params.
DAEMON_OPTS="-p timeout_idle=8"
Verify (windows)
To verify that keepalive is working, check your netstat command in windows. You should have one TCP connection to your varnish. if the sourceport keeps changing your keepalive does not work and your computer is opening new http connections to your varnish for each request. if the sourceport is constant youre browser is using the same TCP connection for all its requests.
This command checks your netstat each 8th second and look for connections to your server at port 80.
while (1) {netstat -no | findstr your-server-ip:80; sleep 8}
Flags for netstat
-n dont do dns lookup (faster)
-o show process id for conenction (in this case firefox PID)
Benefits
Below is a test against one of the varnish server with keepalive configured at 8 seconds same as the .ts chunk files. and with keepalive unconfigured, using its default 5 seconds keepalive. The Round trip time to the server using ping was 25ms. A correct configured keepalive returns the result at average 23ms faster than an unconfigured keepalive.
| Keepalive Configured | Keepalive Configured | Keepalive Configured | Keepalive Configured | Keepalive Unconfigured | Keepalive Unconfigured | Keepalive Unconfigured | Keepalive Unconfigured |
| 379 | 372 | 382 | 373 | 413 | 371 | 371 | 372 |
| 376 | 373 | 370 | 378 | 421 | 371 | 376 | 371 |
| 374 | 373 | 371 | 397 | 392 | 369 | 373 | 373 |
| 414 | 397 | 400 | 422 | 440 | 428 | 444 | 427 |
| 402 | 421 | 399 | 423 | 442 | 422 | 427 | 428 |
| 423 | 422 | 434 | 421 | 467 | 450 | 449 | 447 |
| 436 | 425 | 425 | 424 | 469 | 452 | 455 | 451 |
| 426 | 433 | 422 | 423 | 457 | 456 | 451 | 451 |
| 397 | 394 | 399 | 397 | 440 | 428 | 424 | 425 |
| 426 | 428 | 429 | 425 | 446 | 475 | 474 | 476 |
| 425 | 426 | 421 | 426 | 469 | 453 | 454 | 451 |
| 407,09 | 405,82 | 404,73 | 409,91 | 441,45 | 425 | 427,09 | 424,73 |