I should add that this isn't the first time this has happened, but it is the first time since I reduced the allocation of RAM for PostgreSQL in the configuration file. I swore that that was the problem, but I guess not. It's been almost a full week without any usage spikes or service interruptions of this kind, but all of a sudden, my RAM and CPU are maxing out again at regular intervals. When this occurs, the instance is unreachable until the issue resolves itself, which seemingly takes 5-10 minutes.
The usage spikes only started today out of a seven-day graph; they are far above my idle usage.
I thought the issue was something to do with Lemmy periodically fetching some sort of remote data and slamming the database, which is why I reduced the RAM allocation for PostgreSQL to 1.5 GB instead of the full 2 GB. As you can see in the above graph, my idle resource utilization is really low. Since it's probably cut off from the image, I'll add that my disk utilization is currently 25-30%. Everything seemed to be in order for basically an entire week, but this problem showed up again.
Does anyone know what is causing this? Clearly, something is happening that is loading the server more than usual.
Oh, and for completeness:
We've deleted the vast majority of the spam bots that spammed our instance, are currently on closed registration with applications, and have had no anomalous activity since.
Our server is essentially always at 50% memory (1GB/2GB), 10% CPU (2 vCPUs), and 30% disk (15-20GB/60GB) until a spike. Disk utilization does not change during a spike.
Our instance is relatively quiet, and we probably have no more than ten truly active users at this point. We have a potential uptick in membership, but this is still relatively slow and negligible.
This issue has happened before, but I assumed it was fixed when I changed the PostgreSQL configuration to utilize less RAM. This is still the longest lead-up time before the spikes started.
When the spike resolves itself, the instance works as expected. The issues with service interruptions seems to stem from a drastic increase in resource utilization, which could be caused by some software component that I'm not aware of. I used the Ansible install for Lemmy, and have only modified certain configuration files as required. For the most part, I've only added a higher max_client_body_size in the nginx configs for larger images, and have added settings for an SMTP relay to the main config.hjson file. The spikes occured before these changes, which leads me to believe that they are caused by something I have not yet explored.
These issues occured on both 0.17.4 and 0.18.0, which seems to indicate it's not a new issue stemming from a recent source code change.