Docker just to not fall over when Docker wouldn’t immediately give it 4GB
Funny that you mention that. I tried my hardest to get it running in Docker, and wanted the latest version (8.x). And, like you said, it just would never start.
However, it was hard to configure because it came with security settings and wanted to run over HTTPS on a local connection, which didn't make much sense (as I blocked incoming 9200/9300 ports anyway, so it's communicating locally).
So, I did more research before giving up and found that Elasticsearch 7 doesn't require the certificates to be registered. Though, for security, I did update the username "elastic"'s password to something more hardened, just in case.
I am running Elasticsearch 7.10.2 in Docker and it's taking half the RAM.
The server instance isn't that busy, so I didn't want to upgrade to 4 GB RAM until necessary. It has 0 effect on responsiveness with the forums running. It's constantly at 60-70% usage, but no problems so far.
A 1 vCPU, 2 GB RAM, 55 GB, 2 TB bandwidth with Plesk Admin ($12.95 after 1st month) and auto-backups ($2/mo) comes to a total of $24.95/mo beginning the 2nd month (1st month is $12).
You can save $12.95 by choosing a free control panel like CyberPanel FastPanel, or Webmin and $2 if you remember to manually backup or set up automated backup FTP transfers to your computer.
So, you could hypothetically pay as little as $10 for an instance that would run Elasticsearch just fine with multiple forums on it. I, on the other hand, would choose to use AMD High Performance, which is 1 vCPU, 2 GB RAM, 50 GB NVMe (faster file read speeds), and 3 TB bandwidth for a base price of $12 (add $2 backups and $12.95 if you choose Plesk).
Compare that to GoDaddy 1 vCPU, 2 GB RAM, 40 GB NVMe with cPanel or Plesk for $36.98/mo (although you get 1 additional IP which is like $2 or $4 at Vultr) and 7 snapshots for daily backups for a week (which would be like $5 at Vultr).
I would consider my proposition low-tier and cost-saving compared to one of the largest hosts. You might get something similar to GoDaddy (with a reseller or lesser-known/lower-trust service) for $20-25, but you'd still be essentially paying double.
If you want to try out Vultr for a month, I believe it's free if you install the lowest tier (which is only 1 GB RAM, so you couldn't test out Elasticsearch), but it could get you a feel for Plesk or the other panels if you're a cPanel user for free, feel free to use my promo code
Vultr Global Cloud Hosting - Brilliantly Fast SSD VPS Cloud Servers. 100% KVM Virtualization
www.vultr.com
If you feel Vultr is right for you after a month and make a $100 deposit, you'll get a $300 credit to your account (I'll get $100*). With $400 deposited, and the bare bones of what I suggested, you could run "free" for 60 days (as the $300 credit expires if you don't use it, but you could put it to use by trying out a lot of different instance configurations for what is right for you with it) and then your $100 deposited would be about a year of hosting paid. *If you just pay $10 to test it out, I'll get $10.
* $10 for $10 promo link:
Vultr Global Cloud Hosting - Brilliantly Fast SSD VPS Cloud Servers. 100% KVM Virtualization
www.vultr.com
Vultr also has a nice built in firewall that would've prevented the recent Cyberpanel attacks if configured, and, free DNS management that is awesome and updates quickly once changes are made (like within seconds if you need to enter a TXT record for Amazon or Google verification). In addition to that, they have Object Storage that is S3 compatible, so you can use that with Xenforo's native support with 1 TB starting at $5.
That said, try the Elasticsearch 7.10.2 image on your current VPS. It should boot right up without issue and you shouldn't notice any performance issues whatsoever if you have less than 4GB (2GB is required as I did test it to try and limit it to 1GB and 1.5GB).
Just to add, if you didn't know, Xenforo Cloud uses Vultr. So, it's not a service I'd turn my head to vs. Linode or Amazon S3.