Kubernetes--Pod management and configuration apiversion: v1kind: configmapmetadata: Name: cm appvarsdata: apploglevel:

Posted by apocryia on Sun, 07 Nov 2021 01:28:18 +0100

1, Configuration management of Pod
      The best practice of application deployment is to separate the configuration information required by the application from the program, so that the application can be reused better, and better functions can be realized through different configurations. After the application is packaged into a container image, configuration injection can be carried out when creating a container through environment variables or plug-in files. However, in a large-scale container environment, different configurations of multiple containers will become very complex. K8S provides a unified configuration management scheme - ConfigMap in version 1.2.
1.ConfigMap overview
      Typical usage of ConfigMap for containers:
        (1)   Generate environment variables within the container
        (2) Set the container startup command startup parameters (to be set as environment variables)
        (3) Mount as volume inside the container
        ConfigMap is saved in the K8S system in the form of one or more key: values. It can be used to represent the value of a variable (for example, apploglevel=info) or the content of a complete configuration file (for example, server. XML = <? XML >). ConfigMap can be created through YAML file or kubectl create configmap command line.
2. Create ConfigMap resource object
  • Create from yaml file
  • apiVersion: v1
kind: ConfigMap
metadata:
  name: cm-appvars
data:
  apploglevel: info
  appdatadir: /var/data

  • Define the two configuration files server.xml and logging.properties as ConfigMap:   

  • apiVersion: v1
kind: ConfigMap
metadata:
  name: cm-appconfigfiles
data:
  key-serverxml: |
    <?xml version='1.0' encoding='utf-8'?>
    <Server port="8005" shutdown="SHUTDOWN">
      <Listener className="org.apache.catalina.startup.VersionLoggerListener" />
      <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
      <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />
      <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
      <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />
      <GlobalNamingResources>
        <Resource name="UserDatabase" auth="Container"
                  type="org.apache.catalina.UserDatabase"
                  description="User database that can be updated and saved"
                  factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
                  pathname="conf/tomcat-users.xml" />
      </GlobalNamingResources>

      <Service name="Catalina">
        <Connector port="8080" protocol="HTTP/1.1"
                   connectionTimeout="20000"
                   redirectPort="8443" />
        <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
        <Engine name="Catalina" defaultHost="localhost">
          <Realm className="org.apache.catalina.realm.LockOutRealm">
            <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
                   resourceName="UserDatabase"/>
          </Realm>
          <Host name="localhost"  appBase="webapps"
                unpackWARs="true" autoDeploy="true">
            <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
                   prefix="localhost_access_log" suffix=".txt"
                   pattern="%h %l %u %t &quot;%r&quot; %s %b" />

          </Host>
        </Engine>
      </Service>
    </Server>
  key-loggingproperties: "handlers
    = 1catalina.org.apache.juli.FileHandler, 2localhost.org.apache.juli.FileHandler,
    3manager.org.apache.juli.FileHandler, 4host-manager.org.apache.juli.FileHandler,
    java.util.logging.ConsoleHandler\r\n\r\n.handlers = 1catalina.org.apache.juli.FileHandler,
    java.util.logging.ConsoleHandler\r\n\r\n1catalina.org.apache.juli.FileHandler.level
    = FINE\r\n1catalina.org.apache.juli.FileHandler.directory = ${catalina.base}/logs\r\n1catalina.org.apache.juli.FileHandler.prefix
    = catalina.\r\n\r\n2localhost.org.apache.juli.FileHandler.level = FINE\r\n2localhost.org.apache.juli.FileHandler.directory
    = ${catalina.base}/logs\r\n2localhost.org.apache.juli.FileHandler.prefix = localhost.\r\n\r\n3manager.org.apache.juli.FileHandler.level
    = FINE\r\n3manager.org.apache.juli.FileHandler.directory = ${catalina.base}/logs\r\n3manager.org.apache.juli.FileHandler.prefix
    = manager.\r\n\r\n4host-manager.org.apache.juli.FileHandler.level = FINE\r\n4host-manager.org.apache.juli.FileHandler.directory
    = ${catalina.base}/logs\r\n4host-manager.org.apache.juli.FileHandler.prefix =
    host-manager.\r\n\r\njava.util.logging.ConsoleHandler.level = FINE\r\njava.util.logging.ConsoleHandler.formatter
    = java.util.logging.SimpleFormatter\r\n\r\n\r\norg.apache.catalina.core.ContainerBase.[Catalina].[localhost].level
    = INFO\r\norg.apache.catalina.core.ContainerBase.[Catalina].[localhost].handlers
    = 2localhost.org.apache.juli.FileHandler\r\n\r\norg.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager].level
    = INFO\r\norg.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager].handlers
    = 3manager.org.apache.juli.FileHandler\r\n\r\norg.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/host-manager].level
    = INFO\r\norg.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/host-manager].handlers
    = 4host-manager.org.apache.juli.FileHandler\r\n\r\n"

    • Create from the command line

          You can directly create a ConfigMap through kubectl create configmap, or you can specify the content using the parameters -- from file or -- from literal, and you can specify multiple parameters in one line of command.

       (1) Create from a file with the -- from file parameter. You can specify a key name or create configmaps for multiple keys on one command line 
    kubectl create config NAME --from-file=[key=] source --from-file=[key=] source

    2) Create in the directory through the -- from file parameter. The name of each configuration file in the directory is set to key, and the content of the file is set to value,

    kubectl create configmap NAME --from-file=config-files-dir

    (3) When using -- from literal, it will be created from the text, and the directly specified key#=value # will be created as the ConfigMap content

    kubectl create configmap NAME --from-literal=key1=value1 --from-literal=key2=value2

    3. Use ConfigMap resource object in Pod     Set the contents of "cm appvars" in ConfigMap as the environment variables inside the container in the form of environment variables, and the container startup command displays these two environment variables

    apiVersion: v1
kind: Pod
metadata:
  name: cm-test-pod
spec:
  containers:
  - name: cm-test
    image: busybox
    command: [ "/bin/sh", "-c", "env | grep APP" ]
    env:
    - name: APPLOGLEVEL        #Defines the name of the environment variable
      valueFrom:
        configMapKeyRef:
          name: cm-appvars    #Environment variables are taken from cm appvars
          key: apploglevel    #key is the value corresponding to apploglevel
    - name: APPDATADIR        #Define environment variable name
      valueFrom:
        configMapKeyRef:
          name: cm-appvars   #Environment variables are taken from cm appvars
          key: appdatadir    #The key is appdatadir
  restartPolicy: Never

    Viewing the Pod log, you can see that the ConfigMap value is configured correctly

        kubernetes introduces a new field envFrom from version 1.6 to automatically generate the key=value defined in configmap (which can also be used for Secret resource object) into an environment variable in the Pod environment.  

    apiVersion: v1
kind: Pod
metadata:
  name: cm-test-pod
spec:
  containers:
  - name: cm-test
    image: busybox
    command: [ "/bin/sh", "-c", "env" ]
    envFrom:
    - configMapRef
       name: cm-appvars   #Automatically generate environment variables according to cm appvars
  restartPolicy: Never

    Using ConfigMap through volumeMount

    apiVersion: v1
kind: Pod
metadata:
  name: cm-test-app
spec:
  containers:
  - name: cm-test-app
    image: kubeguide/tomcat-app:v1
    ports:
    - containerPort: 8080
    volumeMounts:
    - name: serverxml             #The name of the reference volume
      mountPath: /configfiles     #Mount to the directory inside the container
  volumes:
  - name: serverxml               #Defines the name of the volume
    configMap:
      name: cm-appconfigfiles     #Use ConfigMap "cm appconfigfiles"
      items:
      - key: key-serverxml       #Use key = key serverxml
        path: server.xml         #value mount server.xml
      - key: key-loggingproperties #Use key = key logging properties
        path: logging.properties   #value mount logging.properties

        Enter Pod   The CM test app container in cm test app can see two mounted files in the / configfile directory.

    4. Restrictions on using ConfigMap

    ConfigMap must be created before pod before pod can reference it    ConfigMap is limited by namespace. Only pods in the same namespace can reference it. ConfigMap cannot be used for static pods. If pod uses evnFrom to define environment variables based on ConfigMap, invalid environment variable names will be ignored and recorded in the event

Topics: Docker Kubernetes Container

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