Hey! I’ve installed dev version of RouterOS to launch Pihole but I guess that I have the wrong architecture on my router.
System-Resources says I have mips cpu but there are ony arm/arm64 /amd64 versions of docker images.
Am I able to use pihole or no chance?
You need to find a MIPS compatible image !
Found a compiled Image of Pihole for MIPS searching on Google
Don’t know if they work yet
In theory you can build any custom container for use with docker on ROS. But yes, you need container image prepared for architecture of router where you want to run the container.
I guess most container images will be available for ARM, ARM64 and AMD64 platforms as they are common, they are powerful and development environments are readily available. hAP lite uses MMIPS platform and devices based on this platform are rare nowdays, even less support development tools needed to build container image.
Pretty sure there are pleanty of people that were excited about the docker implementation in ROS7 and would like to try pihole on their MIPS routers.
I know I would 
Hope this post develops further with answers and maybe a specific MT MIPS build.
I guess we’ll have to wait for containers built for low-memory boxes. Most containers nowdays don’t care about RAM (and disk) requirements, some containers are too greedy to comfortably run on devices with only 32 MB RAM (such as hAP lite) of which half is already needed by ROS itself … even if device supports USB storage for hosting container image.
Only routers with beefier CPUs and RAM will be able to run containers comfortably, for users with budget devices it will be better to go for a Raspberry Pi 4 with a quad-core ARM64 processor and 2-8GB RAM costing between 40€ and 84€ and USB/SD storage, a few GB will do.