Kubernetes config map symlinks (..data/) : is there a way to avoid them?

问题

I have noticed that when I create and mount a config map that contains some text files, the container will see those files as symlinks to ../data/myfile.txt .

For example, if my config map is named tc-configs and contains 2 xml files named stripe1.xml and stripe2.xml, if I mount this config map to /configs in my container, I will have, in my container :

bash-4.4# ls -al /configs/
total 12
drwxrwxrwx    3 root     root          4096 Jun  4 14:47 .
drwxr-xr-x    1 root     root          4096 Jun  4 14:47 ..
drwxr-xr-x    2 root     root          4096 Jun  4 14:47 ..2018_06_04_14_47_03.291041453
lrwxrwxrwx    1 root     root            31 Jun  4 14:47 ..data -> ..2018_06_04_14_47_03.291041453
lrwxrwxrwx    1 root     root            18 Jun  4 14:47 stripe1.xml -> ..data/stripe1.xml
lrwxrwxrwx    1 root     root            18 Jun  4 14:47 stripe2.xml -> ..data/stripe2.xml

I guess Kubernetes requires those symlinks and ../data and ..timestamp/ folders, but I know some applications that can fail to startup if they see non expected files or folders

Is there a way to tell Kubernetes not to generate all those symlinks and directly mount the files ?

回答1:

I think this solution is satisfactory : specifying exact file path in mountPath, will get rid of the symlinks to ..data and ..2018_06_04_19_31_41.860238952

So if I apply such a manifest :

apiVersion: v1
kind: Pod
metadata:
  name: my-lamp-site
spec:
    containers:
    - name: php
      image: php:7.0-apache
      volumeMounts:
      - mountPath: /var/www/html/users.xml
        name: site-data
        subPath: users.xml
    volumes:
    - name: site-data
      configMap:
        name: users

---

apiVersion: v1
kind: ConfigMap
metadata:
  name: users
data:
  users.xml: |
      <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
      <users>
      </users>

Apparently, I'm making use of subpath explicitly, and they're not part of the "auto update magic" from ConfigMaps, I won't see any more symlinks :

$ kubectl exec  my-lamp-site -c php -- ls -al /var/www/html
total 12
drwxr-xr-x 1 www-data www-data 4096 Jun  4 19:18 .
drwxr-xr-x 1 root     root     4096 Jun  4 17:58 ..
-rw-r--r-- 1 root     root       73 Jun  4 19:18 users.xml

Be careful to not forget subPath, otherwise users.xml will be a directory !

Back to my initial manifest :

spec:
    containers:
    - name: php
      image: php:7.0-apache
      volumeMounts:
      - mountPath: /var/www/html
        name: site-data
    volumes:
    - name: site-data
      configMap:
        name: users

I'll see those symlinks coming back :

$ kubectl exec  my-lamp-site -c php -- ls -al /var/www/html
total 12
drwxrwxrwx 3 root root 4096 Jun  4 19:31 .
drwxr-xr-x 3 root root 4096 Jun  4 17:58 ..
drwxr-xr-x 2 root root 4096 Jun  4 19:31 ..2018_06_04_19_31_41.860238952
lrwxrwxrwx 1 root root   31 Jun  4 19:31 ..data -> ..2018_06_04_19_31_41.860238952
lrwxrwxrwx 1 root root   16 Jun  4 19:31 users.xml -> ..data/users.xml

Many thanks to psycotica0 on K8s Canada slack for putting me on the right track with subpath (they are quickly mentioned in configmap documentation)

回答2:

I am afraid I don't know if you can tell Kubernetes not to generate those symlinks although I think that it is a native behaviour.

If having those files and links is an issue, a workaround that I can think of is to mount the configmap on one folder and copy the files over to another folder when you initialise the container:

  initContainers:
    - name: copy-config
      image: busybox
      command: ['sh', '-c', 'cp /configmap/* /configs']
      volumeMounts:
        - name: configmap
          mountPath: /configmap
        - name: config
          mountPath: /configs

But you would have to declare two volumes, one for the configMap (configmap) and one for the final directory (config):

  volumes:
    - name: config
      emptyDir: {}
    - name: configmap
      configMap:
        name: myconfigmap

Change the type of volume for the config volume as you please obviously.

来源：https://stackoverflow.com/questions/50685385/kubernetes-config-map-symlinks-data-is-there-a-way-to-avoid-them

标签

Kubernetes

configmap