Running DC/OS on Small Digital Ocean Droplets | Hacker News Reader

Running DC/OS on Small Digital Ocean Droplets

penguindreams.org

53 pointsdjsumdog8 comments

Great write up!

I've had similar experience with startup and installation while running on Packet with much more beefy machines. Overall, DCOS is really nice to have but it is not without it's headaches so far.

I switched off as soon as I saw 'swapon'

> I switched off as soon as I saw 'swapon'

Why? We're discussing running systems with as little at 512MB of RAM, but have 60GB of HDD.

Swap may not be as fast as RAM, but it's sure a heck of a lot better than crashing when your system needs 513MB for an instant...

"Although swap is generally recommended for systems utilizing traditional spinning hard drives, using swap with SSDs can cause issues with hardware degradation over time. Due to this consideration, we do not recommend enabling swap on DigitalOcean or any other provider that utilizes SSD storage. Doing so can impact the reliability of the underlying hardware for you and your neighbors. This guide is provided as reference for users who may have spinning disk systems elsewhere.

If you need to improve the performance of your server on DigitalOcean, we recommend upgrading your Droplet. This will lead to better results in general and will decrease the likelihood of contributing to hardware issues that can affect your service."

1) Hardware degradation is not for you to worry about as a user. That's for DigitalOcean (or any other cloud provider) to worry about. You specifically pay them so you don't have to worry about hardware issues.

2) I have serious doubts that a rarely-used small 512MB swap file is going to degrade hardware and lead to performance issues for either your VM or your neighbors. Even if it did, see point #1 above.

> Doing so can impact the reliability of the underlying hardware for you and your neighbors

This sounds like they're concerned about thrashing disk I/O... to which I'd say it sounds like they've under-spec'd/over-sold the host server if one VM swapping can degrade performance for all guests. Do they not have upper-bounded I/O quotas or I/O balancing? Can a single VM doing heavy disk I/O that is not Swap cause the same performance degradation? It seems so...

> If you need to improve the performance of your server on DigitalOcean

No, having Swap is not about improving performance, it's about keeping your system up and running in the rare event it exceeds the allocated RAM. Kernel Panics are not fun, and it's generally better to run with reduced-performance than not to run at all - at least until the Admin has time to make the appropriate changes to either rein-in the runaway RAM usage, or upgrade to more RAM.

> we recommend upgrading your Droplet

They would recommend that, wouldn't they...

I would argue (and personally prefer) the opposite. The OOM killer reaping your application is easy to diagnose (it's logged) and it is obvious what you need to do to fix it. Random slowdowns due to it hitting swap could be very hard to debug if they cause issues.

IMO, running on so little resources only makes very limited sense. The underlying Mesos Agent service and the other DC/OS services require memory as well, so that very little memory will be left to schedule tasks on.

Having swap space will not help as far as I know, because Mesos will not consider it as "available memory".

"I wanted to see what was involved in setting up my own DC/OS instance [...] I wanted to keep this cluster as low cost as possible"

Reply on news.ycombinator.com