Tag: Docker

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Raspberry Pi Docker Cluster

I’ve always wanted to experiment with clustering technologies, I tried setting up a kubernetes cluster however that ended in failure. For this next experiment, I went with something simpler to deal with, docker swarm. Since docker and swarm are supported on raspberry pi’s, and since i had a number of raspberry pi’s not in use, I decided to use them for the cluster.

I printed a 2U rack mount kit for raspberry pis. I felt like this would be the perfect time to make use of it. I racked up 2 raspberry pi 3B+ units with POE hats (more on that later) and went to use those for the docker cluster. I added Samsung 32GB micro sd cards for storage.

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Virtualized Docker Swarm

Why

Why not? In reality, I always wanted to play with clustering, originally with proxmox and ceph, but I never had enough hardware to do so. I do however have a proxmox node with enough ram that I can host multiple lightweight nodes.

Docker swarm is lightweight enough that I can virtualize the entire cluster on my single proxmox host. While this isn’t fault tolerant like a cluster across multiple nodes, it does mean I can reboot cluster nodes for kernel updates and maintain my uptime. I also am able to add additional docker swarm nodes on separate hardware if I get additional hardware, and there is the benefit of having the cluster load balance itself for which software is running on which node.

Benefits

Each node in the cluster is identical, each can be replaced by following the exact same process and while I don’t have automated deployment of new nodes, they are still closer to cattle than many of my other virtual machines. Due to the goal of replicated storage between the nodes, I should also be able to take a single node and rebuild the entire cluster if needed, since it would have the entire clusters configuration.

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IRC Botnet and Jenkins

I wrote a number of IRC bots a number of years ago, hosting them on my infrastructure. Since building a 3 node docker swarm, I decided that these would be good candidates to use in learning Jenkins for both auto building the software, and building containers. I hadn’t made my own dockerfiles before, nor had I setup proper builds outside of my IDE for these bots before.

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Docker Struggles

I was originally excited when docker was going to be included in the next release of unraid, the concept behind it was solid and sounded like it would make management of my server easier. This was the case for months before docker started acting up. Now I’ve been working on a way to remove any need of docker on my NAS, moving it to a VM or another server due to its instabilities. Issues I’ve run into include it not being able to stop running containers, start stopped containers, create new containers, and preventing Linux from shutting down. I could live with all of the above except the shutdown bug. It doesn’t just prevent shutdown from running, but it prevents the kernel from shutting down at all, and well after the user shells are all offline, so there’s no way to manually kill docker to allow the system to shut down safely. This is exceptionally frustrating and has caused unclean shutdowns when I’ve lost power and even when I’m just doing maintenance, since the only way to restart when docker does this is to do a hard reset. I’m not giving up hope on containers, just going to be a bit more careful around docker, they seem to advertise quite well compared to issues people have had with their software.