docker-bungeecord VS Purpur

I recommend using itzg's Docker images for this. Run a separate container for each server using itzg/docker-minecraft-server. Then connect them using itzg/docker-bungeecord (also supports Waterfall and Velocity). Put all of these containers in a single Docker Compose so that they will all share the same network for the proxy.

You can use this Docker container to set them up, it supports all of these proxies. itzg also has docker images for Minecraft server , which I am a big fan of, but the BungeeCord/proxy container can work with regular Minecraft servers to as long as they're on the same network.

Ok so I'm using this docker image https://github.com/itzg/docker-bungeecord and I'm trying to interpolate server ip's into a velocity.toml file but it keeps giving me this error

We will be downloading the Minecraft server files into this directory. To preface, there are numerous variations of server JARs that can be used (e.g. Spigot, Paper, Purpur each touting their own benefits). For this tutorial, we will be working with Paper, a fork of Spigot that is optimized for performance.

I Mostly Like Linux as a OS For a Server and PurpurMC (https://purpurmc.org) As a Server Software and i Mostly Use EssentialsX and WorldEdit and More Server Management Stuff.

If you prefer to go the old-school Bukkit/Spigot/Paper/Purpur route (which provides the greatest level of compatibility with pre-existing server plugins), I recommend the latter of the four. Each of these projects is a fork, built on each other in that same order. Each fork offers additional customisation, API, and performance enhancements over its predecessor.

I’d recommend Paper (which is a fork of spigot) or Purpur which is a fork of paper and pufferfish

If you're looking to re-add gravity duping I would recommend not using a plugin but switching your server software to PurpurMC. It is a fork/version of PaperMC that re-adds gravity duping as a config option as well as the ability to toggle back on things like tnt duping and several other features that the PaperMC devs arbitrarily decided were bugs (even though Mojang has explicitly not removed them).

Small addendum:\ If you want to keep using a paper derivative (as a drop-in replacement), you can use purpurMC instead. It provides a config option to enable gravity block duping by disabling sand.fix-duping. (At least for sand)

You can host a small purpur server

Have you tried re-downloading the latest purpur jar file from the purpur website?

tweak some configuration, try lower your entities spawn, I at last you might want to try PurPurMC for the server, it's paper fork with some modification, I feel a lot of improvement since using this fork...