Kubernetes: get actual resource limits from within container

Is there a way to get the actual resource (CPU and memory) constraints from inside a container?

Say the node has 4 cores, but my container is only configured with 1 core through resource requests/limits, so it actually uses 1 core, but it still sees 4 cores from /proc/cpuinfo. I want to determine the number of threads for my application based on the number of cores it can actually use. I'm also interested in memory.

Short answer

You can use the Downward API to access the resource requests and limits. There is no need for service accounts or any other access to the apiserver for this.

Example:

apiVersion: v1
kind: Pod
metadata:
  name: dapi-envars-resourcefieldref
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox:1.24
      command: [ "sh", "-c"]
      args:
      - while true; do
          echo -en '\n';
          printenv MY_CPU_REQUEST MY_CPU_LIMIT;
          printenv MY_MEM_REQUEST MY_MEM_LIMIT;
          sleep 10;
        done;
      resources:
        requests:
          memory: "32Mi"
          cpu: "125m"
        limits:
          memory: "64Mi"
          cpu: "250m"
      env:
        - name: MY_CPU_REQUEST
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: requests.cpu
              divisor: "1m"
        - name: MY_CPU_LIMIT
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: limits.cpu
              divisor: "1m"
        - name: MY_MEM_REQUEST
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: requests.memory
        - name: MY_MEM_LIMIT
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: limits.memory
  restartPolicy: Never

Test:

$ kubectl logs dapi-envars-resourcefieldref
125
250
33554432
67108864

Long answer

Kubernetes translates resource requests and limits to kernel primitives. It is possible to access that information from the pod too, but considerably more complicated and also not portable (Window$ nodes, anyone?)

• CPU requests/limits: /sys/fs/cgroup/cpu/kubepods/..QOS../podXX/cpu.* : cpu.shares (this is requests; divide by 1024 to get core percentage), cpu.cfs_period_us, cpu.cfs_quota_us (divide cfs_quota_us by cfs_period_us to get cpu limit, relative to 1 core)
• Memory limit: /sys/fs/cgroup/memory/kubepods/..QOS../podXX/memory.limit_in_bytes
• Memory request: this one is tricky. It gets translated into oom adjustment scores under /proc/..PID../oom_score_adj . Good luck calculating that back to memory request amount :)

Short answer is great, right? ;)