Connecting to a Service

Building on top of the Go quickstart guide, this guide will connect a service to the Go application.

Prerequisites

1. Install the Service Binding Operator via Operator Hub. Read why this is required.

2. Install Percona Server Mongodb Operator via Operator Hub.

   note

   This operator is namespace scoped, so it will only be accessible in the namespace where it has been installed.

   When you install the operator by following Operator Hub instructions, the operator will be installed in a new namespace called "my-percona-server-mongodb-operator".

3. Create a MongoDB service.

   note

   The service should be created in the namespace where Percona Server Mongodb Operator is installed, in this case, it will be "my-percona-server-mongodb-operator".

Kubernetes

cat << EOF | kubectl apply -f -
apiVersion: psmdb.percona.com/v1-11-0
kind: PerconaServerMongoDB
metadata:
  name: mongodb-instance
  namespace: my-percona-server-mongodb-operator
spec:
  crVersion: 1.11.0
  image: 'percona/percona-server-mongodb:4.4.10-11'
  secrets:
    users: mongodb-instance-secrets
  replsets:
    - name: rs0
      size: 1
      resources:
        limits:
          cpu: 300m
          memory: 0.5G
        requests:
          cpu: 300m
          memory: 0.5G
      volumeSpec:
        persistentVolumeClaim:
          resources:
            requests:
              storage: 1Gi
  sharding:
    enabled: true
    configsvrReplSet:
      size: 1
      resources:
        limits:
          cpu: 300m
          memory: 0.5G
        requests:
          cpu: 300m
          memory: 0.5G
      volumeSpec:
        persistentVolumeClaim:
          resources:
            requests:
              storage: 1Gi
    mongos:
      size: 1
EOF

OpenShift

cat << EOF | oc apply -f -
apiVersion: psmdb.percona.com/v1-11-0
kind: PerconaServerMongoDB
metadata:
  name: mongodb-instance
  namespace: my-percona-server-mongodb-operator
spec:
  crVersion: 1.11.0
  image: 'percona/percona-server-mongodb:4.4.10-11'
  secrets:
    users: mongodb-instance-secrets
  replsets:
    - name: rs0
      size: 1
      resources:
        limits:
          cpu: 300m
          memory: 0.5G
        requests:
          cpu: 300m
          memory: 0.5G
      volumeSpec:
        persistentVolumeClaim:
          resources:
            requests:
              storage: 1Gi
  sharding:
    enabled: true
    configsvrReplSet:
      size: 1
      resources:
        limits:
          cpu: 300m
          memory: 0.5G
        requests:
          cpu: 300m
          memory: 0.5G
      volumeSpec:
        persistentVolumeClaim:
          resources:
            requests:
              storage: 1Gi
    mongos:
      size: 1
EOF

Step 1. Implement the code logic

note

If you are already running odo dev in the terminal, press "Ctrl+c" and exit.

We will extend the current code logic to obtain the connection information (username, password, and host) from the environment and then use it to connect to the MongoDB service and ping it.

The environment variables will be exposed when we link our application with the MongoDB service.

Replace the content of your main.go with the following content:

package main

import (
    "context"
    "fmt"
    "net/http"
    "os"

    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
    "go.mongodb.org/mongo-driver/mongo/readpref"
)

// Connection URI
var (
    USERNAME = os.Getenv("PERCONASERVERMONGODB_MONGODB_USER_ADMIN_USER")
    PASSWORD = os.Getenv("PERCONASERVERMONGODB_MONGODB_USER_ADMIN_PASSWORD")
    HOST     = os.Getenv("PERCONASERVERMONGODB_HOST")
    uri      = fmt.Sprintf("mongodb://%s:%s@%s:27017/?maxPoolSize=20&w=majority", USERNAME, PASSWORD, HOST)
)

func main() {
    http.HandleFunc("/", HelloServer)
    http.ListenAndServe("0.0.0.0:8080", nil)
}

func HelloServer(w http.ResponseWriter, r *http.Request) {
    // Create a new client and connect to the server
    client, err := mongo.Connect(context.TODO(), options.Client().ApplyURI(uri))

    if err != nil {
        fmt.Fprintf(w, "failed to connect: %s", err.Error())
        return
    }
    defer func() {
        if err = client.Disconnect(context.TODO()); err != nil {
            fmt.Fprintf(w, "failed to disconnect: %s", err.Error())
            return
        }
    }()

    // Ping the primary
    if err := client.Ping(context.TODO(), readpref.Primary()); err != nil {
        fmt.Fprintf(w, "unable to connect to the server: %s", err.Error())
        return
    }

    fmt.Fprintf(w, "Successfully connected and pinged.")
}

We will be using the MongoDB client library. Update the go.mod dependency by running the following command:

go get go.mongodb.org/mongo-driver/mongo

Step 2. Run the application

Run the application on the cluster with odo dev.

odo dev

Sample output:

$ odo dev
  __
 /  \__     Developing using the my-go-app Devfile
 \__/  \    Namespace: odo-dev
 /  \__/    odo version: v3.0.0-rc1
 \__/

↪ Running on the cluster in Dev mode
•  Waiting for Kubernetes resources  ...
⚠  Pod is Pending
✓  Pod is Running
✓  Syncing files into the container [152ms]
✓  Building your application in container on cluster (command: build) [15s]
•  Executing the application (command: run)  ...
-  Forwarding from 127.0.0.1:40001 -> 8080


Watching for changes in the current directory /tmp/go
Press Ctrl+c to exit `odo dev` and delete resources from the cluster

Pushing files...


File /tmp/go/.odo changed
•  Waiting for Kubernetes resources  ...
✓  Syncing files into the container [1ms]

Watching for changes in the current directory /tmp/go
Press Ctrl+c to exit `odo dev` and delete resources from the cluster

Check the connection

Once the application is running, query the URL and check the response.

curl 127.0.0.1:40001

Sample output:

$ curl 127.0.0.1:40001
failed to connect: error validating uri: username required if URI contains user info

You should have received an error in response which is expected as we have not yet exposed the connection information in our application.

Step 3. Connect the application to the MongoDB service

Connect the application to the MongoDB service with odo add binding.

From a new terminal, run the following command that will add necessary data to devfile.yaml:

odo add binding \
  --service mongodb-instance/PerconaServerMongoDB \
  --service-namespace=my-percona-server-mongodb-operator \
  --name my-go-app-mongodb-instance \
  --bind-as-files=false

Sample output:

$ odo add binding --service mongodb-instance/PerconaServerMongoDB --service-namespace=my-percona-server-mongodb-operator --name my-go-app-mongodb-instance --bind-as-files=false
 ✓  Successfully added the binding to the devfile.
Run `odo dev` to create it on the cluster.

note

Our code logic relies on obtaining connection information from the environment variables in the system and --binding-as-files=false ensures that. Read here to know more about this flag.

Wait for odo dev to detect the new changes to devfile.yaml.

Sample output:

$ odo dev
  __
 /  \__     Developing using the my-go-app Devfile
 \__/  \    Namespace: odo-dev
 /  \__/    odo version: v3.0.0-rc1
 \__/

↪ Running on the cluster in Dev mode
•  Waiting for Kubernetes resources  ...
⚠  Pod is Pending
✓  Pod is Running
✓  Syncing files into the container [152ms]
✓  Building your application in container on cluster (command: build) [15s]
•  Executing the application (command: run)  ...
-  Forwarding from 127.0.0.1:40001 -> 8080


Watching for changes in the current directory /tmp/go
Press Ctrl+c to exit `odo dev` and delete resources from the cluster

Pushing files...


File /tmp/go/.odo changed
•  Waiting for Kubernetes resources  ...
✓  Syncing files into the container [1ms]

Watching for changes in the current directory /tmp/go
Press Ctrl+c to exit `odo dev` and delete resources from the cluster

Pushing files...


File /tmp/go/devfile.yaml changed
•  Waiting for Kubernetes resources  ...
✓  Creating kind ServiceBinding
Error occurred on Push - watch command was unable to push component: some servicebindings are not injected

Updating Component...

•  Waiting for Kubernetes resources  ...
Error occurred on Push - watch command was unable to push component: some servicebindings are not injected

⚠  Pod is Terminating
•  Waiting for Kubernetes resources  ...
✗  Finished executing the application (command: run) [1m]
⚠  No pod exists
⚠  Pod is Pending
✓  Pod is Running
✓  Syncing files into the container [170ms]
✓  Building your application in container on cluster (command: build) [192ms]
•  Executing the application (command: run)  ...
-  Forwarding from 127.0.0.1:40001 -> 8080


Watching for changes in the current directory /tmp/go
Press Ctrl+c to exit `odo dev` and delete resources from the cluster

Pushing files...


File /tmp/go/devfile.yaml changed

File /tmp/go/.odo/devstate.json changed
•  Waiting for Kubernetes resources  ...
✓  Syncing files into the container [1ms]

Watching for changes in the current directory /tmp/go
Press Ctrl+c to exit `odo dev` and delete resources from the cluster

Once odo dev has completed its task, you can run odo describe binding from a new terminal to obtain all the MongoDB service related information that has been exposed to your application:

odo describe binding --name my-go-app-mongodb-instance

Sample output:

$ odo describe binding --name my-go-app-mongodb-instance
Service Binding Name: my-go-app-mongodb-instance
Services:
 •  mongodb-instance (PerconaServerMongoDB.psmdb.percona.com) (namespace: my-percona-server-mongodb-operator)
Bind as files: false
Detect binding resources: true
Available binding information:
 •  PERCONASERVERMONGODB_MONGODB-KEY
 •  PERCONASERVERMONGODB_MONGODB_CLUSTER_MONITOR_USER
 •  PERCONASERVERMONGODB_USERNAME
 •  PERCONASERVERMONGODB_CLUSTERIP
 •  PERCONASERVERMONGODB_MONGODB_CLUSTER_MONITOR_PASSWORD
 •  PERCONASERVERMONGODB_MONGODB_USER_ADMIN_USER
 •  PERCONASERVERMONGODB_PASSWORD
 •  PERCONASERVERMONGODB_HOST
 •  PERCONASERVERMONGODB_MONGODB_USER_ADMIN_PASSWORD
 •  PERCONASERVERMONGODB_PROVIDER
 •  PERCONASERVERMONGODB_TYPE
 •  PERCONASERVERMONGODB_MONGODB_BACKUP_PASSWORD
 •  PERCONASERVERMONGODB_MONGODB_BACKUP_USER
 •  PERCONASERVERMONGODB_MONGODB_CLUSTER_ADMIN_PASSWORD
 •  PERCONASERVERMONGODB_MONGODB_CLUSTER_ADMIN_USER

Step 4. Check the connection again

Query the URL again for a successful connection:

curl 127.0.0.1:40001

Sample output:

$ curl 127.0.0.1:40001
Successfully connected and pinged.

Step 5. Exit and cleanup

• Press Ctrl+c to exit odo dev.

• Remove the binding from devfile.yaml with odo remove binding.

  odo remove binding --name my-go-app-mongodb-instance

• Delete the MongoDB instance that we created at the beginning.

Kubernetes

kubectl delete PerconaServerMongoDB mongodb-instance --namespace my-percona-server-mongodb-operator

OpenShift

oc delete PerconaServerMongoDB mongodb-instance --namespace my-percona-server-mongodb-operator