kubernetes之configmap,深度解析mountPath,subPath,key,path的关系和作用

参考：https://www.cnblogs.com/breezey/p/6582082.html

我们知道，在几乎所有的应用开发中，都会涉及到配置文件的变更，比如说在web的程序中，需要连接数据库，缓存甚至是队列等等。而我们的一个应用程序从写第一行代码开始，要经历开发环境、测试环境、预发布环境只到最终的线上环境。而每一个环境都要定义其独立的各种配置。如果我们不能很好的管理这些配置文件，你的运维工作将顿时变的无比的繁琐。为此业内的一些大公司专门开发了自己的一套配置管理中心，如360的Qcon，百度的disconf等。kubernetes也提供了自己的一套方案，即ConfigMap。kubernetes通过ConfigMap来实现对容器中应用的配置管理。

1.创建configmap

1.1 通过yaml创建

我们先来看第一种，在yaml文件中，配置文件以key-value键值对的形式保存，当然也可以直接放一个完整的配置文件，在下面的示例中，cache_hst、cache_port、cache_prefix即是key-value键值对，而app.properties和my.cnf都是配置文件：

[root@k8s-master k8s-objs]# pwd
/root/k8s-objs
[root@k8s-master k8s-objs]# cat configmap-test1.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: test-cfg
  namespace: default
data:
  cache_host: mysql-k8s
  cache_port: ""
  cache_prefix: k8s
  my.cnf: |
    [mysqld]
    log-bin = mysql-bin
  app.properties: |
    property. = value-
    property. = value-
    property. = value-
[root@k8s-master k8s-objs]#
[root@k8s-master k8s-objs]# kubectl create -f configmap-test1.yaml
configmap/test-cfg created

[root@k8s-master k8s-objs]# kubectl get configmaps
NAME       DATA   AGE
test-cfg         85s
[root@k8s-master k8s-objs]# kubectl describe pod test-cfg
Error from server (NotFound): pods "test-cfg" not found
[root@k8s-master k8s-objs]# kubectl describe configmap test-cfg
Name:         test-cfg
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
app.properties:
----
property. = value-
property. = value-
property. = value-

cache_host:
----
mysql-k8s
cache_port:
----

cache_prefix:
----
k8s
my.cnf:
----
[mysqld]
log-bin = mysql-bin

Events:  <none>
[root@k8s-master k8s-objs]# 

1.2 通过命令创建configmap

kubectl create configmap test-config3 --from-literal=db.host=10.5.10.116 --from-literal=db.port='3306'

##直接将文件创建为configmap

##kubectl create configmap test-config --from-file=./configs ##将该目录下的所有配置文件创建为configmap
##kubectl create configmap test-config2 --from-file=./configs/db.conf --from-file=./configs/cache.conf

[root@k8s-master k8s-objs]# kubectl create configmap test-config3 --from-literal=db.host=10.5.10.116 --from-literal=db.port=''
configmap/test-config3 created
[root@k8s-master k8s-objs]# kubectl get configmaps
NAME           DATA   AGE
test-cfg             6m1s
test-config3         9s
[root@k8s-master k8s-objs]# kubectl describe configmap test-cfg3
Error from server (NotFound): configmaps "test-cfg3" not found
[root@k8s-master k8s-objs]# kubectl describe configmap test-config3
Name:         test-config3
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
db.host:
----
10.5.10.116
db.port:
----

Events:  <none>
[root@k8s-master k8s-objs]# 

查看属性

[root@k8s-master k8s-objs]# kubectl get configmaps -o yaml
apiVersion: v1
items:
- apiVersion: v1
  data:
    app.properties: |
      property. = value-
      property. = value-
      property. = value-
    cache_host: mysql-k8s
    cache_port: ""
    cache_prefix: k8s
    my.cnf: |
      [mysqld]
      log-bin = mysql-bin
  kind: ConfigMap
  metadata:
    creationTimestamp: "2019-04-11T08:25:13Z"
    name: test-cfg
    namespace: default
    resourceVersion: ""
    selfLink: /api/v1/namespaces/default/configmaps/test-cfg
    uid: 544cc424-5c33-11e9-a5c3-000c291ae345

###第二个configmap
- apiVersion: v1
  data:
    db.host: 10.5.10.116
    db.port: ""
  kind: ConfigMap
  metadata:
    creationTimestamp: "2019-04-11T08:31:05Z"
    name: test-config3
    namespace: default
    resourceVersion: ""
    selfLink: /api/v1/namespaces/default/configmaps/test-config3
    uid: 261ab5e2-5c34-11e9-a5c3-000c291ae345
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

2 使用configmap

2.1 作为环境变量

[root@k8s-master k8s-objs]# cat pod-configmap-testenv.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap
  name: testenv
spec:
  containers:
    - name: test-configmap
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      env:
        - name: MY_CACHE_HOST
          valueFrom:
            configMapKeyRef:
              name: test-cfg
              key: cache_host
[root@k8s-master k8s-objs]#
[root@k8s-master k8s-objs]# kubectl create -f pod-configmap-testenv.yaml
pod/testenv created
root@k8s-master k8s-objs]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
hello-5cd4456b66-gstq6   1/1     Running   1          8d
hello-5cd4456b66-sb5px   1/1     Running   1          8d
testenv                  1/1     Running   0          7s

#查看containerid
[root@k8s-master k8s-objs]# kubectl describe pod testenv
Name:               testenv
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               k8s-node1/192.168.111.131
Start Time:         Fri, 12 Apr 2019 08:28:27 +0800
Labels:             purpose=test-configmap
Annotations:        <none>
Status:             Running
IP:                 10.244.1.69
Containers:
  test-configmap:
    Container ID:   docker://7c76ff1602561c498a537ea0bcd3bb0a244a7ef9ec3cdc34b6ba03577d889a93
    Image:          tomcat:8
    Image ID:       docker-pullable://tomcat@sha256:3e3d18321127bb9114f4226f95802d3899aeec4c36df84d0359e5da300e9bc72
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Fri, 12 Apr 2019 08:28:33 +0800
    Ready:          True
    Restart Count:  0
    Environment:
      MY_CACHE_HOST:  <set to the key 'cache_host' of config map 'test-cfg'>  Optional: false
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-92rjn (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-92rjn:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-92rjn
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From                Message
  ----    ------     ----   ----                -------
  Normal  Scheduled  2m49s  default-scheduler   Successfully assigned default/testenv to k8s-node1
  Normal  Pulled     2m44s  kubelet, k8s-node1  Container image "tomcat:8" already present on machine
  Normal  Created    2m44s  kubelet, k8s-node1  Created container test-configmap
  Normal  Started    2m43s  kubelet, k8s-node1  Started container test-configmap
[root@k8s-master k8s-objs]# 

进入kubernetes中的pod的容器中,

kubectl exec -it testenv -n default -- /bin/bash #退出exit

[root@k8s-master k8s-objs]# kubectl exec -it testenv -n default -- /bin/bash ##下面标红表示新的pod主机名，即已成功进入pod
root@testenv:/usr/local/tomcat#
root@testenv:/usr/local/tomcat# echo $MY_CACHE_HOST #查看环境变量是否生效
mysql-k8s
root@testenv:/usr/local/tomcat# exit

2.2 挂载文件数据卷

2.2.1使用volume将ConfigMap作为文件或目录直接挂载，其中每一个key-value键值对都会生成一个文件，key为文件名，value为内容

查看configmap

[root@k8s-master k8s-objs]# kubectl get configmap
NAME           DATA   AGE
test-cfg             16h
test-config3         16h
[root@k8s-master k8s-objs]# kubectl get configmap test-cfg -o yaml
apiVersion: v1
data:
  app.properties: |
    property. = value-
    property. = value-
    property. = value-
  cache_host: mysql-k8s
  cache_port: ""
  cache_prefix: k8s
  my.cnf: |
    [mysqld]
    log-bin = mysql-bin
kind: ConfigMap
metadata:
  creationTimestamp: "2019-04-11T08:25:13Z"
  name: test-cfg
  namespace: default
  resourceVersion: ""
  selfLink: /api/v1/namespaces/default/configmaps/test-cfg
  uid: 544cc424-5c33-11e9-a5c3-000c291ae345
[root@k8s-master k8s-objs]# 

创建pod,并挂载volume

[root@k8s-master k8s-objs]# cat pod-configmap-testvolume.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg

[root@k8s-master k8s-objs]#
[root@k8s-master k8s-objs]# kubectl create -f pod-configmap-testvolume.yaml
pod/testvolume created
[root@k8s-master k8s-objs]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
hello-5cd4456b66-gstq6   /     Running             8d
hello-5cd4456b66-sb5px   /     Running             8d
testvolume               /     Running             113s
[root@k8s-master k8s-objs]# kubectl describe pod testvolume
Name:               testvolume
Namespace:          default
Priority:
PriorityClassName:  <none>
Node:               k8s-node1/192.168.111.131
Start Time:         Fri,  Apr  :: +
Labels:             purpose=test-configmap-volume
Annotations:        <none>
Status:             Running
IP:                 10.244.1.70
Containers:
  test-configmap-volume:
    Container ID:   docker://16de1a9dec62564d6e7e50a3167581e9be8151c388707e8f48f4f5152a0ed83a
    Image:          tomcat:
    Image ID:       docker-pullable://tomcat@sha256:3e3d18321127bb9114f4226f95802d3899aeec4c36df84d0359e5da300e9bc72
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Fri,  Apr  :: +
    Ready:          True
    Restart Count:
    Environment:    <none>
    Mounts:
      /etc/config from config-volume (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-92rjn (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  config-volume:
    Type:      ConfigMap (a volume populated by a ConfigMap)
    Name:      test-cfg
    Optional:  false
  default-token-92rjn:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-92rjn
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From                Message
  ----    ------     ----   ----                -------
  Normal  Scheduled  2m45s  default-scheduler   Successfully assigned default/testvolume to k8s-node1
  Normal  Pulled     2m42s  kubelet, k8s-node1  Container image "tomcat:8" already present on machine
  Normal  Created    2m42s  kubelet, k8s-node1  Created container test-configmap-volume
  Normal  Started    2m42s  kubelet, k8s-node1  Started container test-configmap-volume
[root@k8s-master k8s-objs]# 

进入kubernetes的pod,

[root@k8s-master k8s-objs]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
hello-5cd4456b66-gstq6   /     Running             8d
hello-5cd4456b66-sb5px   /     Running             8d
testvolume               /     Running             3m56s
[root@k8s-master k8s-objs]# kubectl exec -it testsvolume /bin/bash
Error from server (NotFound): pods "testsvolume" not found
[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls
app.properties  cache_host  cache_port  cache_prefix  my.cnf
root@testvolume:/etc/config# ll
bash: ll: command not found
root@testvolume:/etc/config# ls -l ##对照发现，使用volume将ConfigMap作为文件或目录直接挂载，其中每一个key-value键值对都会生成一个文件，key为文件名，value为内容
total
lrwxrwxrwx  root root  Apr  : app.properties -> ..data/app.properties
lrwxrwxrwx  root root  Apr  : cache_host -> ..data/cache_host
lrwxrwxrwx  root root  Apr  : cache_port -> ..data/cache_port
lrwxrwxrwx  root root  Apr  : cache_prefix -> ..data/cache_prefix
lrwxrwxrwx  root root  Apr  : my.cnf -> ..data/my.cnf
root@testvolume:/etc/config# cat app.properties
property. = value-
property. = value-
property. = value-
root@testvolume:/etc/config# cat cache_host
mysql-k8sroot@testvolume:/etc/config# cat cache_port
root@testvolume:/etc/config# cat cache_prefix
k8sroot@testvolume:/etc/config# cat my.cnf
[mysqld]
log-bin = mysql-bin
root@testvolume:/usr/local/tomcat# echo $cache_host ##并没有自动生成环境变量

root@testvolume:/usr/local/tomcat#
root@testvolume:/etc/config# exit

2.2.2 另一种方式，只挂载某个key,并支持相对路径，其中一个key生成的文件路径名和文件名相同

[root@k8s-master k8s-objs]# cat pod-configmap-testvolume.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg
         items:
           - key: cache_host
             path: path/to/special-key-cache #path中的最后一级“special-key-cache”为文件名
           - key: app.properties
             path: app.properties
[root@k8s-master k8s-objs]# kubectl create -f pod-configmap-testvolume.yaml
pod/testvolume created
[root@k8s-master k8s-objs]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
hello-5cd4456b66-gstq6   /     Running             8d
hello-5cd4456b66-sb5px   /     Running             8d
testvolume               /     Running             12s
[root@k8s-master k8s-objs]# kubectl describe pod testvolume
Name:               testvolume
Namespace:          default
Priority:
PriorityClassName:  <none>
Node:               k8s-node1/192.168.111.131
Start Time:         Fri,  Apr  :: +
Labels:             purpose=test-configmap-volume
Annotations:        <none>
Status:             Running
IP:                 10.244.1.71
Containers:
  test-configmap-volume:
    Container ID:   docker://227d2ab39823087193f1830309c73af5408c85f634eb5c7fce9c668533766b76
    Image:          tomcat:
    Image ID:       docker-pullable://tomcat@sha256:3e3d18321127bb9114f4226f95802d3899aeec4c36df84d0359e5da300e9bc72
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Fri,  Apr  :: +
    Ready:          True
    Restart Count:
    Environment:    <none>
    Mounts:
      /etc/config from config-volume (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-92rjn (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  config-volume:
    Type:      ConfigMap (a volume populated by a ConfigMap)
    Name:      test-cfg
    Optional:  false
  default-token-92rjn:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-92rjn
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From                Message
  ----    ------     ----   ----                -------
  Normal  Scheduled  2m27s  default-scheduler   Successfully assigned default/testvolume to k8s-node1
  Normal  Pulled     2m24s  kubelet, k8s-node1  Container image "tomcat:8" already present on machine
  Normal  Created    2m23s  kubelet, k8s-node1  Created container test-configmap-volume
  Normal  Started    2m23s  kubelet, k8s-node1  Started container test-configmap-volume
[root@k8s-master k8s-objs]# 

进入pod

[root@k8s-master k8s-objs]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
hello-5cd4456b66-gstq6   /     Running             8d
hello-5cd4456b66-sb5px   /     Running             8d
testvolume               /     Running             3m24s
[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls -l #在目录/etc/config下生成一个文件（/etc/config/app.properties）和一个带path目录的文件(/etc/config/path/to/special-key-cache)
total
lrwxrwxrwx  root root  Apr  : app.properties -> ..data/app.properties
lrwxrwxrwx  root root  Apr  : path -> ..data/path
root@testvolume:/etc/config# ls app.properties
app.properties
root@testvolume:/etc/config# cat app.properties/app.properties
cat: app.properties/app.properties: Not a directory
root@testvolume:/etc/config# cd app.properties
bash: cd: app.properties: Not a directory
root@testvolume:/etc/config# cat app.properties ##说明key:app.properties的path项用文件名相当于没有起任何作用
property. = value-
property. = value-
property. = value-
root@testvolume:/etc/config# pwd
/etc/config
root@testvolume:/etc/config# cd path/to/special-key-cache
bash: cd: path/to/special-key-cache: Not a directory
root@testvolume:/etc/config# cd path
root@testvolume:/etc/config/path# cd to
root@testvolume:/etc/config/path/to# cd special-key-cache
bash: cd: special-key-cache: Not a directory
root@testvolume:/etc/config/path/to# pwd
/etc/config/path/to
root@testvolume:/etc/config/path/to# ls
special-key-cache
root@testvolume:/etc/config/path/to# cat special-key-cache
mysql-k8sroot@testvolume:/etc/config/path/to# exit

configmap在pod容器中成功生成了文件

3 深度解析mountPath,subPath,key,path的关系和作用

结论：

kubernetes key (pod.spec.volums[0].configMap.items[0].key)用于指定configMap中的哪些条目可用于挂载,如2.2.2

kubernetes path (pod.spec.volums[0].configMap.items[0].path)用于将key重命名，如案例3.3

kubernetes suPath (pod.spec.containers[0].volumeMounts.subPath)决定容器中有无挂载（按名字从key，有path时以path为主，中比对是否存在要的条目）。

kubernetes mountPath (pod.spec.containers[0].volumeMounts.mountPath)决定容器中挂载的结果文件名。没有subPath项时如案例2.2.1，此项仅指定路径。有subPath时且subPath筛选结果为true时如案例3.1，此项指定路径和文件名，此时文件名可随意指定如案例3.4和3.5；有subPath但subPath筛选结果为false时如案例3.2，此项指定路径（最后一级目录名为文件名）

3.1 mountPath结合subPath作用

有subPath时且subPath推荐筛选结果为true，mountPath指定到文件名

注：subPath只是将volume.items.key中多个key进行筛选，只挂载需要的文件，相当于2.2.2中app.properties保留，其它key不挂载

[root@k8s-master k8s-objs]# cat pod-configmap-testvolume.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config/app.properties #此处配合suPath使用时，app.properties为文件名，即pod容器中只生成了/etc/config目录，目录之下 为文件，只有一个名为app.properties的文件（subPath筛选只挂载app.properties文件）
          subPath: app.properties
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg
         items:
           - key: cache_host
             path: path/to/special-key-cache
           - key: app.properties
             path: app.properties
[root@k8s-master k8s-objs]# kubectl create -f pod-configmap-testvolume.yaml
pod/testvolume created
[root@k8s-master k8s-objs]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
hello-5cd4456b66-gstq6   /     Running             8d
hello-5cd4456b66-sb5px   /     Running             8d
testvolume               /     Running             17s
[root@k8s-master k8s-objs]#
[root@k8s-master k8s-objs]# kubectl describe pod testvolume
Name:               testvolume
Namespace:          default
Priority:
PriorityClassName:  <none>
Node:               k8s-node1/192.168.111.131
Start Time:         Fri,  Apr  :: +
Labels:             purpose=test-configmap-volume
Annotations:        <none>
Status:             Running
IP:                 10.244.1.72
Containers:
  test-configmap-volume:
    Container ID:   docker://ef581eaaf8bd895bce8d4e77f66b8c704b557dee186bf72e00e1aa3dbb7390f4
    Image:          tomcat:
    Image ID:       docker-pullable://tomcat@sha256:3e3d18321127bb9114f4226f95802d3899aeec4c36df84d0359e5da300e9bc72
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Fri,  Apr  :: +
    Ready:          True
    Restart Count:
    Environment:    <none>
    Mounts:
      /etc/config/app.properties from config-volume (rw,path="app.properties")
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-92rjn (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  config-volume:
    Type:      ConfigMap (a volume populated by a ConfigMap)
    Name:      test-cfg
    Optional:  false
  default-token-92rjn:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-92rjn
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From                Message
  ----    ------     ----   ----                -------
  Normal  Scheduled  2m13s  default-scheduler   Successfully assigned default/testvolume to k8s-node1
  Normal  Pulled     2m10s  kubelet, k8s-node1  Container image "tomcat:8" already present on machine
  Normal  Created    2m10s  kubelet, k8s-node1  Created container test-configmap-volume
  Normal  Started    2m10s  kubelet, k8s-node1  Started container test-configmap-volume
[root@k8s-master k8s-objs]# 

进入pod

[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls
app.properties
root@testvolume:/etc/config# ll
bash: ll: command not found
root@testvolume:/etc/config# ls
app.properties
root@testvolume:/etc/config# ls -l
total
-rw-r--r--  root root  Apr  : app.properties
root@testvolume:/etc/config# cd app.properties
bash: cd: app.properties: Not a directory
root@testvolume:/etc/config# cat app.properties
property.1 = value-1
property.2 = value-2
property.3 = value-3
root@testvolume:/etc/config# 

3.2有subPath但筛选结果为false,

容器中生成一个空目录/etc/config/app.properties，无文件

解析。subPath筛选范围优先级为pod.spec.volums[0].configMap.items[0].path>pod.spec.volums[0].configMap.items[0].key>configMap.key，本例中为path,即在path指定的条目【“cache_host”,"app-properties "注意中间是横杠不是点】找是否有subPath项“app.properties”注意中间为点，查找结果为false,所以无文件挂载。容器将“/etc/config/app.properties”当成一个待创建的路径。

[root@k8s-master k8s-objs]# vi pod-configmap-testvolume.yaml

apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config/app.properties #此时此处app.properties为文件名
          subPath: app.properties
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg
         items:
           - key: cache_host
             path: path/to/special-key-cache
           - key: app.properties
             path: app-properties #此处path相当于更改文件名mv app.properties app-properties 
[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls
app.properties
root@testvolume:/etc/config# ll #此目录下只有一个子目录
bash: ll: command not found
root@testvolume:/etc/config# ls -l
total
drwxrwxrwx  root root  Apr  : app.properties
root@testvolume:/etc/config# cat app.properties
cat: app.properties: Is a directory
root@testvolume:/etc/config# cd app.properties
root@testvolume:/etc/config/app.properties# ls
root@testvolume:/etc/config/app.properties# ls #此目录下为空
root@testvolume:/etc/config/app.properties# 

3.3无 subPath,path相当于重命名

[root@k8s-master k8s-objs]# cat pod-configmap-testvolume.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config/app.properties ##此处app.properties为目录
#          subPath: app.properties
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg
         items:
           - key: cache_host
             path: path/to/special-key-cache
           - key: app.properties
             path: app-properties #此处path相当于更改文件名mv app.properties app-properties
[root@k8s-master k8s-objs]#
[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# ls
BUILDING.txt  CONTRIBUTING.md  LICENSE  NOTICE  README.md  RELEASE-NOTES  RUNNING.txt  bin  conf  include  lib  logs  native-jni-lib  temp  webapps  work
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls
app.properties
root@testvolume:/etc/config# ls -l
total
drwxrwxrwx  root root  Apr  : app.properties
root@testvolume:/etc/config# cd app.properties
root@testvolume:/etc/config/app.properties# ls
app-properties  path
root@testvolume:/etc/config/app.properties# ls -l
total
lrwxrwxrwx  root root  Apr  : app-properties -> ..data/app-properties
lrwxrwxrwx  root root  Apr  : path -> ..data/path
root@testvolume:/etc/config/app.properties# cat app-properties
property. = value-
property. = value-
property. = value-
root@testvolume:/etc/config/app.properties# cat path
cat: path: Is a directory
root@testvolume:/etc/config/app.properties# cd path
root@testvolume:/etc/config/app.properties/path# ls
to
root@testvolume:/etc/config/app.properties/path# cd to
root@testvolume:/etc/config/app.properties/path/to# ls -l
total
-rw-r--r--  root root  Apr  : special-key-cache
root@testvolume:/etc/config/app.properties/path/to# cat special-key-cache
mysql-k8sroot@testvolume:/etc/config/app.properties/path/to# 

3.4有subPath且筛选结果为true,mouthPath指定文件名，可以和subPath不一样

[root@k8s-master k8s-objs]# vi pod-configmap-testvolume.yaml

apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config/app.properties #此处app.properties为文件名
          subPath: app-properties #改为与mountPath不一样的文件名时，subPath相当于通过volume筛选configMap中的key(此处为因volumes.configMap.items.path对key进行了重命名)中的条目，即存在subPath时，subPath决定有无，mountPath决定文件名
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg
         items:
           - key: cache_host
             path: path/to/special-key-cache
           - key: app.properties
             path: app-properties

[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls
app.properties
root@testvolume:/etc/config# ls -l
total
-rw-r--r--  root root  Apr  : app.properties
root@testvolume:/etc/config# cat app.properties
property. = value-
property. = value-
property. = value-
root@testvolume:/etc/config# pwd
/etc/config
root@testvolume:/etc/config# ls
app.properties
root@testvolume:/etc/config# exit

3.5有subPath且筛选结果为true,mouthPath指定文件名，可以和subPath不一样，甚至随意指定为z.txt

[root@k8s-master k8s-objs]# vi pod-configmap-testvolume.yaml

apiVersion: v1
kind: Pod
metadata:
  labels:
    purpose: test-configmap-volume
  name: testvolume
spec:
  containers:
    - name: test-configmap-volume
      image: tomcat:
      imagePullPolicy: IfNotPresent
      #command: [ "/bin/sh", "-c", "echo $(MY_CACHE_HOST)" ]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config/z.txt #subPath决定有无，mountPath决定文件名为z.txt
          subPath: app-properties
  volumes:
    - name: config-volume
      configMap:
         name: test-cfg
         items:
           - key: cache_host
             path: path/to/special-key-cache
           - key: app.properties
             path: app-properties

[root@k8s-master k8s-objs]# kubectl exec -it testvolume /bin/bash
root@testvolume:/usr/local/tomcat# cd /etc/config
root@testvolume:/etc/config# ls
z.txt
root@testvolume:/etc/config# pwd
/etc/config
root@testvolume:/etc/config# cat z.txt
property. = value-
property. = value-
property. = value-
root@testvolume:/etc/config#