Displaying Docker containers and their history with Go
Even in the age of newfangled buzzwords like "Kubernetes," veteran system administrators still appreciate command-line tools like good old top, which displays running processes in real time. Since I also want to keep up with the young bloods (even at my age, which can already be described as advanced), I recently created a small, terminal-based monitor that shows Docker containers coming and going on a system.
The standard Docker client, docker, is written in Go and communicates via a web interface with the Docker daemon to query the status of running containers, start new ones, or terminate existing ones. In addition to a Python interface, Docker also offers a Go SDK. Since Go also has excellent libraries for displaying in the terminal, it was my choice for implementing the dockertop monitor in this Programming Snapshot column.
The idea is simple: The program asks the Docker daemon at regular intervals for all the containers running on the system, displays their names in a list, and refreshes them every second – just like top. As an additional treat, the monitor in the right part of the split screen also displays a rolling history of the containers. Each time it detects a new one, the program writes New: <Name> into it. If a container has been lost since the last call – for example, because it has died in the meantime – the log entry reads: Gone: <Name> (Figure 1).
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