Get the currently used and maximum available memory for a Docker container running in Kubernetes

k8s-get-docker-container-memory.sh

# These commands demonstrate how to determine how much memory is availble on a k8s worker node and how much memory is 
# available to the k8s _container_ hosted on that node.
# Source:
#   https://shuheikagawa.com/blog/2017/05/27/memory-usage/
#
# Other interesting articles:
#   https://docs.docker.com/engine/docker-overview/#the-underlying-technology
#   https://docs.docker.com/config/containers/resource_constraints/
#
# These values are approximations, because according to the first article, calculating/determining available memory 
# is difficult.
#
# In this example, the k8s deployment file is set with the following resource requests and limits values:

cat my-deployment-file.yml
spec:
  # ...
  template:
    # ...
    spec:
      containers:
      - name: [name of container]
        image: [image]
        resources:
          requests:
            cpu: 200m
            memory: 1024M
          limits:
            cpu: 400m
            memory: 2048M

# Get a shell onto the pod
kubectl exec -it [valid pod name in your k8s cluster] -- /bin/sh

# Get the memory available on the node:
/ # free -m
             total       used       free     shared    buffers     cached
Mem:          7986       6940       1045          0        552       3978
-/+ buffers/cache:       2409       5577
Swap:            0          0          0

# Get the memory usage of the container (in bytes)
/ # cat /sys/fs/cgroup/memory/memory.usage_in_bytes
443748352 (443748352/1024^2 ~= 423.19MB)

# Get the memory limit of the container (in bytes)
/ # cat /sys/fs/cgroup/memory/memory.limit_in_bytes
2048000000  (2048000000/1024^3 ~= 1953.13MB)