Kondense

Kondense is an automated resource sizing tool. It runs as a sidecar in kubernetes pods.

Background

Memory

Kondense uses memory pressure to apply just the right amount of memory on a container to page out the unused memory while not getting out-of-memory killed.
How is memory calculated ?

CPU

Kondense resizes CPU based on CPU usage, default to 80%.
How is CPU calculated ?

Requirements

On Kubernetes

• The Kubernetes cluster must run on Linux.
• Containerd version >= 1.6.9.
• Kubernetes should have the feature gate InPlacePodVerticalScaling enabled.

On Containers

• Containers should include the linux kernel version >= 4.20. Ensure the file /sys/fs/cgroup/memory.pressure exists in the container to verify it.

You can build your containers from the image alpine to be sure.

Example

Try the example on minikube:

minikube start --kubernetes-version=v1.29.2 --feature-gates=InPlacePodVerticalScaling=true
kubectl apply -f https://raw.githubusercontent.com/unagex/kondense/main/example/nginx.yaml

Let's say we have a pod running nginx that we want to Kondense:

apiVersion: v1
kind: Pod
metadata:
  name: kondense-test
spec:
  serviceAccountName: nginx-user
  containers:
  - name: nginx
    image: nginx:latest
    resources:
      limits:
        cpu: 100m
        memory: 100M

Add Kondense as a sidecar:

apiVersion: v1
kind: Pod
metadata:
  name: kondense-test
spec:
  serviceAccountName: nginx-user
  containers:
  - name: nginx
    image: nginx:latest
    resources:
      limits:
        cpu: 0.1
        memory: 100M
  - name: kondense
    image: kondense/kondense:1.1.0
    resources:
      limits:
        cpu: 80m
        memory: 50M

After adding the kondense container, the nginx container resources are updated without any container restart.

Notes:

1. The pod should have a QoS of Guaranteed. In other words, we need to add resources limits for each containers.
2. The service account nginx-user should have the following rules:

rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["get", "list", "watch", "patch"]
  - apiGroups: [""]
    resources: ["pods/exec"]
    verbs: ["create"]

Configuration

Kondense is configurable via environment variables in the kondense container.

Example

    ...
    - name: kondense
      image: kondense/kondense:1.1.0
      resources:
        limits:
          cpu: 80m
          memory: 50M
      env:
      - name: <CONTAINER NAME>_MEMORY_MIN
        value: "100m"

If we have a container named nginx in our pod, the variable name should be NGINX_MEMORY_MIN.

Environment variables

Global

Name	Default value	Description
EXCLUDE	""	Comma separated list of containers to not kondense.

Memory

Name	Default value	Description
<CONTAINER NAME>_MEMORY_MIN	50M	Minimum memory of the container. Kondense will never resize below that limit.
<CONTAINER NAME>_MEMORY_MAX	100G	Maximum memory of the container. Kondense will never resize above that limit.
<CONTAINER NAME>_MEMORY_TARGET_PRESSURE	10000	Target memory pressure in microseconds. Kondense will take corrective actions to obtain it.
<CONTAINER NAME>_MEMORY_INTERVAL	10	Kondense targets cumulative memory delays over the sampling period of this interval in seconds.
<CONTAINER NAME>_MEMORY_MAX_INC	0.5	Maximum memory increase for one correction. e.g. 0.5 is a 50% increase.
<CONTAINER NAME>_MEMORY_MAX_DEC	0.02	Maximum memory decrease for one correction. e.g. 0.02 is a 2% decrease.
<CONTAINER NAME>_MEMORY_COEFF_INC	20	Coeff to increase memory when the memory pressure is bigger then the target memory pressure.
<CONTAINER NAME>_MEMORY_COEFF_DEC	10	Coeff to decrease memory when the memory pressure is smaller then the target memory pressure.

CPU

Name	Default value	Description
<CONTAINER NAME>_CPU_MIN	0.08	Minimum CPU of the container. Kondense will never resize below that limit.
<CONTAINER NAME>_CPU_MAX	100	Maximum CPU of the container. Kondense will never resize above that limit.
<CONTAINER NAME>_CPU_MAX_INC	0.5	Maximum CPU increase for one correction. e.g. 0.5 is a 50% increase.
<CONTAINER NAME>_CPU_MAX_DEC	0.1	Maximum CPU decrease for one correction. e.g. 0.1 is a 10% decrease.
<CONTAINER NAME>_CPU_TARGET_AVG	0.8	Target CPU average for the container. It is from 0 to 1. e.g. 0.8 means a target cpu usage of 80%.
<CONTAINER NAME>_CPU_INTERVAL	6	CPU interval in seconds to calculate the CPU average. Each interval last 1 second.
<CONTAINER NAME>_CPU_COEFF	6	Used to calculate the new cpu limit when a cpu increase is needed. The higher the coeff, the higher the new cpu limit.

More

• Kondense memory resize is based on Meta Transparent Memory Offloading (TMO)
• Kondense is active on himself by default