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OOMHero

OOMHero is a sidecar that helps you to keep track of your containers memory usage. By implementing it two signals are going to be send to your container as the memory usage grows: a warning and a critical signals. By leveraging these signals you might be able to defeat the deadly OOMKiller.

How it works

This sidecar will send your container two signals: when memory usage crosses so called warning(SIGUSR1 by default) and critical(SIGUSR2 by default) thresholds. It is possible to use different signals by specifying appropriate environment variables. Your application must be able to deal with these signals by implementing signal handlers.

You an see here an example of how to capture the signals in Go.

On limits

If only requests are specified during the pod Deployment no signal will be sent, this sidecar operates only on limits.

Deployment example

The Pod below is composed by two distinct containers, the first one is called bloat and its purpose is(as the name implies) to simulate a memory leak by constantly allocating in a global variable. The sidecar is an OOMHero configured to send a SIGUSR1(warning) when bloat reaches 65% and a SIGUSR2 (critical) on 90%. The only pre-requisite is that both containers share the same process namespace, hence shareProcessNamespace is set to true.

apiVersion: v1
kind: Pod
metadata:
  name: oomhero
spec:
  shareProcessNamespace: true
  containers:
    - name: bloat
      image: quay.io/rmarasch/bloat:latest
      imagePullPolicy: Always
      livenessProbe:
        periodSeconds: 3
        failureThreshold: 1
        httpGet:
          path: /healthz
          port: 8080
      resources:
        requests:
          memory: "256Mi"
          cpu: "250m"
        limits:
          memory: "256Mi"
          cpu: "250m"
    - name: oomhero
      image: quay.io/rmarasch/oomhero:latest
      imagePullPolicy: Always
      securityContext:
        privileged: true
      env:
      - name: WARNING
        value: "65"
      - name: CRITICAL
        value: "90"

Saving the above yaml into a file you just need to deploy it:

$ kubectl create -f ./pod.yaml

That will create a Pod with two containers, you may follow the memory consumption and signals being sent by inspecting all pod logs.

$ # for bloat container log
$ kubectl logs -f oomhero --container bloat
$ # for oomhero container log
$ kubectl logs -f oomhero --container oomhero

Configuring signals

Signals supported by OOMHero are:

  • SIGABRT
  • SIGCONT
  • SIGHUP
  • SIGINT
  • SIGIOT
  • SIGKILL
  • SIGQUIT
  • SIGSTOP
  • SIGTERM
  • SIGTSTP
  • SIGUSR1
  • SIGUSR2

To use any of those signals instead of default ones, set WARNING_SIGNAL and CRITICAL_SIGNAL environment variable to specify warning and critical signals respectively. If those environment variables are not set, OOMHero will use default values (SIGUSR1 and SIGUSR2).

For instance to send SIGTERM when critical threshold is reached put following in pod or deployment definition:

containers:
  # other containers omitted for brevity
  - name: oomhero
    image: quay.io/rmarasch/oomhero
    imagePullPolicy: Always
    env:
    - name: WARNING
      value: "65"
    - name: CRITICAL
      value: "90"
    - name: CRITICAL_SIGNAL
      value: "SIGTERM"

Cooldown

By default OOMHero sends one signal per second to other processes once they reach warning or critical threshold. This might be undesireable behavior in some circumstances, therefore cooldown can be configured. Once set, signal will be sent no more often than once in cooldown for each signal type separately. In other words other processes would not receive more than one warning and one ciritcal signal more often than once in cooldown.

To configure cooldown set COOLDOWN environment variable in deployment definition to a value conforming to time.ParseDuartion:

containers:
  # other containers omitted for brevity
  - name: oomhero
    image: quay.io/rmarasch/oomhero
    imagePullPolicy: Always
    env:
    - name: COOLDOWN
      value: "1m30s"

Help needed

Official documentation states that SYS_PTRACE capability is mandatory when signaling between containers on the same Pod. I could not validate if this is true as it works without it on my K8S cluster. If to make it work you had to add this capability please let me know.