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Table of Contents - Limit Container Memory to 4G, Free or 32G

Popularity：707 ℃/2024-12-09 15:01:47

preamble

Recently a new colleague asked me a question, obviously through the limit to the container memory limit of 4G, why into the container to see the host's memory is still 32G

▶ docker run -it --rm -m 512m ubuntu:18.04 bash
root@ae00bec75ad7:/# free -m 
              total        used        free      shared  buff/cache   available
Mem:          31954       11482        8487        1708       11983       18305
Swap:          2047           0        2047

This question brought back a bubble of memories of the details of the knowledge mentioned in the previous study of "Deep Dive into kubernetes".

environmental preparation

subassemblies releases
operating system Ubuntu 22.04.4 LTS
lxcfs 4.0.3
k8s v1.26.3

Introduction to the principle of lxcfs

  • freeis from/procThe file system fetches the data, but when the container starts up the/procis still the mapped host, so thefreeThe information displayed must be the host's
  • utilizationlxcfsThis problem can be solved, essentially by docker booting the limitations imposed on cpu, memory behavior, manually mounting theproc(modified) filesystems into the container
  • The project is still being updated:lxcfs, from the documentation, the supported file systems are these:
/proc/cpuinfo
/proc/diskstats
/proc/meminfo
/proc/stat
/proc/swaps
/proc/uptime
/proc/slabinfo
/sys/devices/system/cpu/online

Installing lxcfs

1) Install the lxcfs tool directly using apt

▶ sudo apt install lxcfs

2) Deploy to the corresponding directory

sudo mkdir -p /var/lib/lxcfs
sudo lxcfs /var/lib/lxcfs &

After deployment, lxcfs is working as a background process

The docker uses

1. Routine start-up

▶ docker run -it --rm -m 512m ubuntu:18.04 bash
root@ae00bec75ad7:/# free -m 
              total        used        free      shared  buff/cache   available
Mem:          31954       11482        8487        1708       11983       18305
Swap:          2047           0        2047

2. docker using lxcfs

Install lxcfs first

▶ sudo apt install lxcfs

▶ docker run -it --rm -m 512m \
      -v /var/lib/lxcfs/proc/meminfo:/proc/meminfo:rw \
      ubuntu:18.04 bash
root@56e3c146ba4e:/# free -m
              total        used        free      shared  buff/cache   available
Mem:            512           1         510           0           0         510
Swap:             0           0           0

With lxcfs, get docker to correctly recognize the restricted memory

k8s usage

1. Routine start-up

▶ echo '          
apiVersion: v1
kind: Pod
metadata:
  name: wilson-test
spec:
  containers:
  - image: ubuntu:18.04
    imagePullPolicy: IfNotPresent
    command: ["sleep", "33333"]
    name: wilson-test
    resources:
      limits:
        memory: 128Mi
      requests:
        memory: 64Mi
' | kubectl apply -f -
pod/wilson-test created

▶ kubectl get pod 
NAME          READY   STATUS    RESTARTS   AGE
wilson-test   1/1     Running   0          3s

▶ kubectl exec -it wilson-test -- free -m
              total        used        free      shared  buff/cache   available
Mem:          31954       11034        6384        1568       14534       18893
Swap:          2047           0        2047

Using lxcfs

▶ echo '                                                                                                                                                                                                                             
apiVersion: v1                                                                                                                                                                                                                       
kind: Pod
metadata:
  name: wilson-test
spec:
  containers:
  - image: ubuntu:18.04
    imagePullPolicy: IfNotPresent
    command: ["sleep", "33333"]
    name: wilson-test
    resources:
      limits:
        memory: 128Mi
      requests:
        memory: 64Mi
    volumeMounts:
    - mountPath: /proc/meminfo
      name: lxcfs-proc-meminfo
      readOnly: true
  volumes:
  - hostPath:
      path: /var/lib/lxcfs/proc/meminfo
      type: ""
    name: lxcfs-proc-meminfo
' | kubectl apply -f -

pod/wilson-test created

▶ kubectl get pod 
NAME          READY   STATUS    RESTARTS   AGE
wilson-test   1/1     Running   0          2s

▶ kubectl exec -it wilson-test -- free -m
              total        used        free      shared  buff/cache   available
Mem:            128           0         127           0           0         127
Swap:          2047           0        2047

memory limit128malready in force

k8s auto inject lxcfs preset

1. Using k8s preset

  • kubernetes v1.20 removed preset.
  • Some big guy on github made it back with a CRD.podpresetBut it hasn't been updated in 3 years.

2. Use of k8sAdmission Controller

You can also find the big guy ready-made at githublxcfs-admission-webhookBut it doesn't seem to have been updated for a long time.

wrap-up

  • This article only demonstrates memory, about the other metrics, just follow the lead
  • Regarding the automount, the ready-made projects have not been updated for a long time, so you can try to hand rub one in the back.admission-hookHere's to the future.

Contact me

Contact me for an in-depth chat

This concludes this article
I'm not very knowledgeable, so if there is any soup leakage, please do not hesitate to give me advice...

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