Secret

Kubernetes Secrets are used to store sensitive information such as passwords, API keys, and certificates in a secure way. They help separate configuration from application code, improving security and manageability.

Type of Secret

Here are built-in secret type available in kubernetes:

Type	Usage
Opaque:	arbitrary user-defined data.
kubernetes.io/service-account-token:	ServiceAccount token.
kubernetes.io/dockercfg:	serialized ~/.dockercfg file.
kubernetes.io/dockerconfigjson:	serialized ~/.docker/config.json file.
kubernetes.io/basic-auth:	credentials for basic authentication.
kubernetes.io/ssh-auth:	credentials for SSH authentication.
kubernetes.io/tls:	data for a TLS client or server.
bootstrap.kubernetes.io/token:	bootstrap token data.

Opaque Secret

Previously we already create a postgres service with persistent volume. But we still use plain text as the username and password config. We can use secret to properly store the sensitive configuration and use it in our postgres deployment.

Create new file called postgres-secret.yaml and put the secret definition there.

apiVersion: v1
kind: Secret
metadata:
  name: postgres-secret
type: Opaque
data:
  POSTGRES_USER: "YWRtaW4="
  POSTGRES_PASSWORD: "cGFzc3dvcmQ="

The data section contains key value pair of our sensitive data. In here we store 2 data for username and password with key POSTGRES_USERNAME and POSTGRES_PASSWORD respectively. The value of the pair need to be base64 encoded first. We can use command echo -n "admin" | base64 to encode it.

Lets apply and validate our secret.

➜ kubectl apply -f postgres-secret.yaml 
secret/postgres-secret created

➜ kubectl get secret  
NAME              TYPE     DATA   AGE
postgres-secret   Opaque   2      21s

As you can see above the secret is created with DATA length is 2. We also can describe it to see the details.

➜ kubectl describe secrets postgres-secret
Name:         postgres-secret
Namespace:    default
Labels:       <none>
Annotations:  <none>

Type:  Opaque

Data
====
POSTGRES_PASSWORD:  8 bytes
POSTGRES_USER:      5 bytes

Using Secret

Postgres

To use secret in our postgres deployment we need to update our env from plain text to value from secret.

env:
- name: POSTGRES_USER
  value: "admin"
- name: POSTGRES_PASSWORD
  value: "password"

Replace above section with this section below. This will tell kubernetes to look the value from secret with name postgres-secret and key POSTGRES_USER for the user and POSTGRES_PASSWORD for the password.

env:
- name: POSTGRES_USER
  valueFrom:
    secretKeyRef:
      name: postgres-secret
      key: POSTGRES_USER
- name: POSTGRES_PASSWORD
  valueFrom:
    secretKeyRef:
      name: postgres-secret
      key: POSTGRES_PASSWORD

Lets apply and validate if the pods running without error. We can do similar testing like before, by doing port forward and then connect using psql. We should still able to connect and see the data without any error.

admin=# \c mydb
You are now connected to database "mydb" as user "admin".
mydb=# SELECT * FROM message;
 id | content 
----+---------
  1 | Hello!
(1 row)

Simple V2

Then lets update our apps to write and read from the database. You can just copy paste this and then run go get . to download all the dependencies.

package main

import (
    "encoding/json"
    "fmt"
    "log"
    "net/http"
    "os"

    "github.com/gorilla/mux"
    "github.com/jmoiron/sqlx"
    _ "github.com/lib/pq"
)

type Message struct {
    ID      int    `json:"id" db:"id"`
    Content string `json:"content" db:"content"`
}

func main() {
    // Get user and password from env
    user := os.Getenv("POSTGRES_USER")
    password := os.Getenv("POSTGRES_PASSWORD")
    // Database connection
    host := "postgres.default.svc.cluster.local"
    connectionStr := fmt.Sprintf("host=%s user=%s password=%s dbname=mydb sslmode=disable", host, user, password)
    db, err := sqlx.Connect("postgres", connectionStr)
    if err != nil {
        log.Fatal(err)
    }

    // handlers
    mux := mux.NewRouter()
    mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        // fetch data from database
        messages := []Message{}
        err := db.SelectContext(
            r.Context(),
            &messages,
            "SELECT * FROM message",
        )
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        // return it as json response
        err = json.NewEncoder(w).Encode(messages)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
    }).Methods(http.MethodGet)
    mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        // get content from json body
        message := &Message{}
        err := json.NewDecoder(r.Body).Decode(message)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        // save to database
        _, err = db.NamedExecContext(
            r.Context(),
            "INSERT INTO message (content) VALUES (:content)",
            message,
        )
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Write([]byte("SUCCESS"))
    }).Methods(http.MethodPost)

    // start server
    fmt.Println("Server is running on port 8080...")
    err = http.ListenAndServe(":8080", mux)
    if err != nil {
        log.Fatal(err)
    }
}

This app will get user and password configuration from environment variable and use it to connect to the server. And to access our service (postgres) from internal cluster we can use this format <service_name>.<namespace>.svc.cluster.local.

Build our app and tag it as simple-go:v2.

➜ docker build --tag simple-go:v2 .

Update our deployment to use image simple-go:v2 and replace the env with this one below. This will make POSTGRES_USER and POSTGRES_PASSWORD environment variable available in our apps.

env:
- name: POSTGRES_USER
  valueFrom:
    secretKeyRef:
      name: postgres-secret
      key: POSTGRES_USER
- name: POSTGRES_PASSWORD
  valueFrom:
    secretKeyRef:
      name: postgres-secret
      key: POSTGRES_PASSWORD

Apply and check if the pods running as expected.

To test it we can use minkube service command to expose our service. Then run curl to the given url.

➜ curl 'http://localhost:58834'
[{"id":1,"content":"Hello!"}]

We should see our data there. Try to send POST request to insert new data and GET again.

➜ curl -X POST -d '{"content": "Good Morning!"}' 'http://localhost:58834/'
SUCCESS
➜ curl 'http://localhost:58834'                                           
[{"id":1,"content":"Hello!"},{"id":2,"content":"Good Morning!"}]

We should see new data is properly inserted and returned.

References

• https://kubernetes.io/docs/concepts/configuration/secret/
• https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/