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Replacing a $3000/mo Heroku bill with a $55/mo server

(disco.cloud)
804 points jryio | 3 comments | 21 Oct 25 20:28 UTC | HN request time: 0.023s | source
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speedgoose ◴[21 Oct 25 21:12 UTC] No.45661785[source]▶
Looking at the htop screenshot, I notice the lack of swap. You may want to enable earlyoom, so your whole server doesn't go down when a service goes bananas. The Linux Kernel OOM killer is often a bit too late to trigger.

You can also enable zram to compress ram, so you can over-provision like the pros'. A lot of long-running software leaks memory that compresses pretty well.

Here is how I do it on my Hetzner bare-metal servers using Ansible: https://gist.github.com/fungiboletus/794a265cc186e79cd5eb2fe... It also works on VMs.

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levkk ◴[21 Oct 25 21:51 UTC] No.45662183[source]▶
Yeah, no way. As soon as you hit swap, _most_ apps are going to have a bad, bad time. This is well known, so much so that all EC2 instances in AWS disable it by default. Sure, they want to sell you more RAM, but it's also just true that swap doesn't work for today's expectations.

Maybe back in the 90s, it was okay to wait 2-3 seconds for a button click, but today we just assume the thing is dead and reboot.

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bayindirh ◴[21 Oct 25 22:15 UTC] No.45662411[source]▶
This is a wrong belief because a) SSDs make swap almost invisible, so you can have that escape ramp if something goes wrong b) SWAP space is not solely an escape ramp which RAM overflows into anymore.

In the age of microservices and cattle servers, reboot/reinstall might be cheap, but in the long run it is not. A long running server, albeit being cattle, is always a better solution because esp. with some excess RAM, the server "warms up" with all hot data cached and will be a low latency unit in your fleet, given you pay the required attention to your software development and service configuration.

Secondly, Kernel swaps out unused pages to SWAP, relieving pressure from RAM. So, SWAP is often used even if you fill 1% of your RAM. This allows for more hot data to be cached, allowing better resource utilization and performance in the long run.

So, eff it, we ball is never a good system administration strategy. Even if everything is ephemeral and can be rebooted in three seconds.

Sure, some things like Kubernetes forces "no SWAP, period" policies because it kills pods when pressure exceeds some value, but for more traditional setups, it's still valuable.

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adastra22 ◴[21 Oct 25 22:40 UTC] No.45662646[source]▶
What pressure? If your ram is underutilized, what pressure are you talking about?

If the slowest drive on the machine is the SSD, how does caching to swap help?

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1. adgjlsfhk1 ◴[21 Oct 25 22:51 UTC] No.45662734[source]▶
The OS uses almost all the ram in your system (it just doesn't tell you because then users complain that their OS is too ram heavy). The primary thing it uses it for is caching as much of your storage system as possible. (e.g. all of the filesystem metadata and most of the files anyone on the system has touched recently). As such, if you have RAM that hasn't been touched recently, the OS can page it out and make the rest of the system faster.
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2. adastra22 ◴[21 Oct 25 23:47 UTC] No.45663231[source]▶
At the cost of tanking performance for the less frequently used code path. Sometimes it is more important to optimize in ways that minimize worst case performance rather than a marginal improvement to typical work loads. This is often the case for distributed systems, e.g. SaaS backends.
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3. bayindirh ◴[22 Oct 25 10:13 UTC] No.45666977[source]▶
You can request things from Kernel, like pinning cores or telling kernel not swap your pages out (see mlockall() / madvise()).

The easiest way affecting everything running on the system might not be the best or even the correct way to do things.

There's always more than one way to solve a problem.

Reading the Full Manual (TM) is important.