当挂载ConfigMap或Secret到容器内部时，会覆盖原有目录，直接挂载一不小心就会引发很多问题，比如将nginx.conf挂载到/etc/nginx/nginx.conf，如果使用ConfigMap挂载，就会把/etc/nginx这个目录完全覆盖掉，只会留下一个nginx.conf，这样会导致Nginx找不到系统文件，从而导致Nginx无法启动，所以需要使用subPath字段解决挂载覆盖的问题。
一、演示环境准备¶
接下来导出nginx.conf文件进行修改进行挂载覆盖演示
1.创建工作目录
[root@k8s-master01 ~]# mkdir -p configmap/conf
2.编写配置文件
[root@k8s-master01 ~]# vim configmap/conf/redis.conf
Password=123
3.创建ConfigMap，,其中--from-file参数用于指定文件
[root@k8s-master01 ~]# kubectl create cm cmfromfile --from-file=/root/configmap/conf/redis.conf
configmap/cmfromfile created
4.验证
[root@k8s-master01 ~]# kubectl get cm
NAME DATA AGE
cmfromdir 2 7m18s
cmfromfile 1 2m21s
kube-root-ca.crt 1 25h
[root@k8s-master01 ~]# kubectl get cm cmfromfile -oyaml
apiVersion: v1
data:
redis.conf: |
Password=123
kind: ConfigMap
metadata:
creationTimestamp: "2022-12-03T08:19:26Z"
name: cmfromfile
namespace: default
resourceVersion: "33521"
uid: acf5f51a-5cd8-413e-bf81-14a779b2f2fa
[root@k8s-master01 ~]# kubectl describe cm cmfromfile
Name: cmfromfile
Namespace: default
Labels: <none>
Annotations: <none>
Data
====
redis.conf:
----
Password=123
BinaryData
====
Events: <none>
5.编写dp-cm.yaml
[root@k8s-master01 conf]# vim dp-cm.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: dp-cm
name: dp-cm
spec:
replicas: 1
selector:
matchLabels:
app: dp-cm
template:
metadata:
labels:
app: dp-cm
spec:
containers:
- image: registry.cn-hangzhou.aliyuncs.com/zq-demo/nginx:1.14.2
name: nginx
volumeMounts:
- name: conf
mountPath: /etc/config
volumes:
- name: conf
configMap:
name: cmfromfile
6.创建Pod
$ kubectl create -f dp-cm.yaml
7.导出nginx.conf文件到当前目录下
[root@k8s-master01 conf]# kubectl exec -it dp-cm-6b49968558-bflhj -- cat /etc/nginx/nginx.conf > nginx.conf
8.修改nginx.conf文件，这里只加了注释(演示环境)方便后面演示
[root@k8s-master01 conf]# cat nginx.conf
#test
user nginx;
worker_processes 1;
error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
}
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;
log_format main '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
access_log /var/log/nginx/access.log main;
sendfile on;
#tcp_nopush on;
keepalive_timeout 65;
#gzip on;
include /etc/nginx/conf.d/*.conf;
}
9.查看容器内/etc/nginx/目录下除nginx.conf外还有其他文件
[root@k8s-master01 conf]# kubectl exec -it dp-cm-6b49968558-bflhj -- ls /etc/nginx/ -l
total 68
drwxr-xr-x 1 root root 26 Apr 10 2019 conf.d
-rw-r--r-- 1 root root 1077 Apr 10 2019 fastcgi.conf
-rw-r--r-- 1 root root 1077 Apr 10 2019 fastcgi.conf.default
-rw-r--r-- 1 root root 1007 Apr 10 2019 fastcgi_params
-rw-r--r-- 1 root root 1007 Apr 10 2019 fastcgi_params.default
-rw-r--r-- 1 root root 2837 Apr 10 2019 koi-utf
-rw-r--r-- 1 root root 2223 Apr 10 2019 koi-win
-rw-r--r-- 1 root root 5170 Apr 10 2019 mime.types
-rw-r--r-- 1 root root 5170 Apr 10 2019 mime.types.default
lrwxrwxrwx 1 root root 27 Apr 10 2019 modules -> ../../usr/lib/nginx/modules
-rw-rw-r-- 1 root root 643 Apr 10 2019 nginx.conf
-rw-r--r-- 1 root root 2656 Apr 10 2019 nginx.conf.default
-rw-r--r-- 1 root root 636 Apr 10 2019 scgi_params
-rw-r--r-- 1 root root 636 Apr 10 2019 scgi_params.default
-rw-r--r-- 1 root root 664 Apr 10 2019 uwsgi_params
-rw-r--r-- 1 root root 664 Apr 10 2019 uwsgi_params.default
-rw-r--r-- 1 root root 3610 Apr 10 2019 win-utf
二、演示挂载覆盖¶
上面条件准备完成
1.创建ConfigMap，,其中--from-file参数用于指定文件
$ kubectl create cm nginx-conf --from-file=/root/configmap/conf/nginx.conf
2.修改dp-cm.yaml
$ vim dp-cm.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: dp-cm
name: dp-cm
spec:
replicas: 1
selector:
matchLabels:
app: dp-cm
template:
metadata:
labels:
app: dp-cm
spec:
containers:
- image: registry.cn-hangzhou.aliyuncs.com/zq-demo/nginx:1.14.2
name: nginx
volumeMounts:
- name: conf
mountPath: /etc/nginx/
volumes:
- name: conf
configMap:
name: nginx-conf
3.更新Yaml
$ kubectl delete -f dp-cm.yaml ; kubectl apply -f dp-cm.yaml
4.查看新起的Pod显示Error，并查看日志信息，发现/etc/nginx/目录下的文件都被覆盖
[root@k8s-master01 conf]# kubectl get po
NAME READY STATUS RESTARTS AGE
cluster-test-79b978867f-4x2lw 1/1 Running 101 (5m54s ago) 52d
dp-cm-84d74dcb4b-kpkq4 0/1 Error 2 (17s ago) 19s
[root@k8s-master01 conf]# kubectl logs -f dp-cm-84d74dcb4b-kpkq4
2023/05/03 09:05:12 [emerg] 1#1: open() "/etc/nginx/nginx.conf" failed (2: No such file or directory)
nginx: [emerg] open() "/etc/nginx/nginx.conf" failed (2: No such file or directory)
三、使用SubPath解决挂载覆盖问题¶
1.修改Yaml文件
$ vim dp-cm.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: dp-cm
name: dp-cm
spec:
replicas: 1
selector:
matchLabels:
app: dp-cm
template:
metadata:
labels:
app: dp-cm
spec:
containers:
- image: registry.cn-hangzhou.aliyuncs.com/zq-demo/nginx:1.14.2
name: nginx
volumeMounts:
- name: conf
mountPath: /etc/nginx/nginx.conf
subPath: nginx.conf
volumes:
- name: conf
configMap:
name: nginx-conf
2.重新起Pod
$ kubectl replace -f dp-cm.yaml
3.查看新起的Pod状态
[root@k8s-master01 conf]# kubectl get po
NAME READY STATUS RESTARTS AGE
dp-cm-5478545d-jjhnm 1/1 Running 0 3m12s
4.进入容器查看nginx.conf文件,观察到挂载文件已替换成自己的文件
[root@k8s-master01 conf]# kubectl exec -it dp-cm-5478545d-jjhnm -- cat /etc/nginx/nginx.conf
#test
user nginx;
worker_processes 1;
error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
}
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;
log_format main '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
access_log /var/log/nginx/access.log main;
sendfile on;
#tcp_nopush on;
keepalive_timeout 65;
#gzip on;
include /etc/nginx/conf.d/*.conf;
}