Does this app make any network requests that might have their own cold start or caching effects?

2.5 seconds seems way too long to be attributed to the Worker cold start alone.

It makes requests to API server that is deployed to k8s, which doesn't have a cold start. Clearly, some caching by the runtime and framework is involved here.

My point is that "cold start" is often more than just booting VM instance.

And I noticed not everybody understands it. I used to have conversations in which people argue that there is no difference in deploying web frontend to Cloudflare vs a stateful solution because of this confusing advertisement.

Likely reusing http keep-alive connections.

I'm not well versed with CURL design, but curious - is your first connection handling TLS while second relying on the previously established handshake?

I'm not very well versed with CURL design too but afaik it does reuse connections but only inside the same process (e.g. downloading 10 files with 1 command). In this case it shouldn't be re-using them as I ran 2 different commands. I should have included TLS handshake time in the output, though. You can see it here (overall time is lower because I hit preview env that is slightly different from staging/prod):

First hit: ``` DNS Lookup: 0.026284s Connect (TCP): 0.036498s Time app connect (TLS): 0.059136s Start Transfer: 1.282819s Total: 1.282928s ```

Second hit: ``` DNS Lookup: 0.003575s Connect (TCP): 0.016697s Time app connect (TLS): 0.032679s Start Transfer: 0.242647s Total: 0.242733s ```

Metrics description:

time_namelookup: The time, in seconds, it took from the start until the name resolving was completed.

time_connect: The time, in seconds, it took from the start until the TCP connect to the remote host (or proxy) was completed.

time_appconnect: The time, in seconds, it took from the start until the SSL/SSH/etc connect/handshake to the remote host was completed.

time_starttransfer: The time, in seconds, it took from the start until the first byte was just about to be transferred. This includes time_pretransfer and also the time the server needed to calculate the result.

TLS handshakes (outside of embedded hardware) should be measured in milliseconds, not seconds

Edit: you can kind of tell this from the connect timings listed above. TLS is faster the second time around, but not enough to make much difference to the overall speedup

I think you're right that TLS doesn't explain the difference shown above, but for completeness: TLS 1.3 can reduce the round trips from 3 to 2 on session resumption. [1] Depending on your Internet connection, that could be a lot more than milliseconds. I don't think `curl` uses it by default though.

[1] https://blog.cloudflare.com/introducing-0-rtt/

I would say Cloudflare "eliminated cold starts" in the context of bringing the server online, not in the form of rendering + caching the SSR page.