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Using Custom Configuration File

KubeDB supports providing custom configuration for Memcached. This tutorial will show you how to use KubeDB to run Memcached with custom configuration.

Before You Begin

• At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind.

• Now, install KubeDB cli on your workstation and KubeDB operator in your cluster following the steps here.

• To keep things isolated, this tutorial uses a separate namespace called demo throughout this tutorial.

  $ kubectl create ns demo
  namespace/demo created
  
  $ kubectl get ns demo
  NAME    STATUS  AGE
  demo    Active  5s
  

Note: YAML files used in this tutorial are stored in docs/examples/memcached folder in GitHub repository kubedb/docs.

Overview

Memcached does not allows to configuration via any file. However, configuration parameters can be set as arguments while starting the memcached docker image. To keep similarity with other KubeDB supported databases which support configuration through a config file, KubeDB has added an additional executable script on top of the official memcached docker image. This script parses the configuration file then set them as arguments of memcached binary.

To know more about configuring Memcached server see here.

At first, you have to create a config file named memcached.conf with your desired configuration. Then you have to put this file into a volume. You have to specify this volume in spec.configSecret section while creating Memcached crd. KubeDB will mount this volume into /usr/config directory of the database pod.

In this tutorial, we will configure max_connections and limit_maxbytes via a custom config file. We will use a Secret as volume source.

Configuration File Format: KubeDB support providing memcached.conf file in the following formats,

# maximum simultaneous connection
-c 500
# maximum allowed memory for the database in MB.
-m 128

or

# This is a comment line. It will be ignored.
--conn-limit=500
--memory-limit=128

or

# This is a comment line. It will be ignored.
conn-limit = 500
memory-limit = 128

Custom Configuration

At first, let’s create memcached.conf file setting max_connections and limit_maxbytes parameters. Default value of max_connections is 1024 and limit_maxbytes is 64MB (68157440 bytes).

$ cat <<EOF >memcached.conf
-c 500
# maximum allowed memory in MB
-m 128
EOF

$ cat memcached.conf
-c 500
# maximum allowed memory in MB
-m 128

Note that config file name must be memcached.conf

Now, create a Secret with this configuration file.

 $ kubectl create secret generic -n demo mc-configuration --from-file=./memcached.conf
secret/mc-configuration created

Verify the Secret has the configuration file.

$ kubectl get secrets -n demo mc-configuration -o yaml
apiVersion: v1
stringData:
  memcached.conf: |
    -c 500
    # maximum allowed memory in MB
    -m 128    
kind: Secret
metadata:
  creationTimestamp: 2018-10-04T05:29:37Z
  name: mc-configuration
  namespace: demo
  resourceVersion: "4505"
  selfLink: /api/v1/namespaces/demo/secrets/mc-configuration
  uid: 7c38b5fd-c796-11e8-bb11-0800272ad446

Now, create Memcached crd specifying spec.configSecret field.

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2024.2.14/docs/examples/memcached/configuration/mc-custom.yaml
memcached.kubedb.com/custom-memcached created

Below is the YAML for the Memcached crd we just created.

apiVersion: kubedb.com/v1alpha2
kind: Memcached
metadata:
  name: custom-memcached
  namespace: demo
spec:
  replicas: 1
  version: "1.6.22"
  configSecret:
    name: mc-configuration
  podTemplate:
    spec:
      resources:
        limits:
          cpu: 500m
          memory: 128Mi
        requests:
          cpu: 250m
          memory: 64Mi

Now, wait a few minutes. KubeDB operator will create the necessary deployment, services etc. If everything goes well, we will see that a deployment with the name custom-memcached has been created.

Check that the pods for the deployment is running:

$ kubectl get pods -n demo
NAME                                READY     STATUS    RESTARTS   AGE
custom-memcached-747b866f4b-j6clt   1/1       Running   0          5m

Now, we will check if the database has started with the custom configuration we have provided. We will use stats command to check the configuration.

We will connect to custom-memcached-5b5866f5b8-cbc2d pod from local-machine using port-frowarding.

$ kubectl port-forward -n demo custom-memcached-5b5866f5b8-cbc2d  11211
Forwarding from 127.0.0.1:11211 -> 11211
Forwarding from [::1]:11211 -> 11211

Now, connect to the memcached server from a different terminal through telnet.

$ telnet 127.0.0.1 11211
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
stats
...
STAT max_connections 500
...
STAT limit_maxbytes 134217728
...
END

Here, limit_maxbytes is represented in bytes.

Cleaning up

To cleanup the Kubernetes resources created by this tutorial, run:

kubectl patch -n demo mc/custom-memcached -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
kubectl delete -n demo mc/custom-memcached

kubectl patch -n demo drmn/custom-memcached -p '{"spec":{"wipeOut":true}}' --type="merge"
kubectl delete -n demo drmn/custom-memcached

kubectl delete -n demo secret mc-configuration

kubectl delete ns demo

If you would like to uninstall KubeDB operator, please follow the steps here.

Next Steps

• Learn how to use KubeDB to run a Memcached server here.
• Want to hack on KubeDB? Check our contribution guidelines.