Quickstart: Build a Go app with the gocql client to manage Azure Cosmos DB Cassandra API data

APPLIES TO: Cassandra API

Azure Cosmos DB is a multi-model database service that lets you quickly create and query document, table, key-value, and graph databases with global distribution and horizontal scale capabilities. In this quickstart, you will start by creating an Azure Cosmos DB Cassandra API account. You will then run a Go application to create a Cassandra keyspace, table, and execute a few operations. This Go app uses gocql, which is a Cassandra client for the Go language.

Prerequisites

Create a database account

Before you can create a database, you need to create a Cassandra account with Azure Cosmos DB.

  1. In a new browser window, sign in to the Azure portal.

  2. In the left menu, select Create a resource.

    Create a resource in the Azure portal

  3. On the New page, select Databases > Azure Cosmos DB.

    The Azure portal Databases pane

  4. On the Create Azure Cosmos DB Account page, enter the settings for the new Azure Cosmos DB account.

    Setting Value Description
    Subscription Your subscription Select the Azure subscription that you want to use for this Azure Cosmos DB account.
    Resource Group Create new

    Then enter the same name as Account Name
    Select Create new. Then enter a new resource group name for your account. For simplicity, use the same name as your Azure Cosmos account name.
    Account Name Enter a unique name Enter a unique name to identify your Azure Cosmos DB account. Your account URI will be cassandra.cosmos.azure.com appended to your unique account name.

    The account name can use only lowercase letters, numbers, and hyphens (-), and must be between 3 and 31 characters long.
    API Cassandra The API determines the type of account to create. Azure Cosmos DB provides five APIs: Core (SQL) for document databases, Gremlin for graph databases, MongoDB for document databases, Azure Table, and Cassandra. You must create a separate account for each API.

    Select Cassandra, because in this quickstart you are creating a table that works with the Cassandra API.

    Learn more about the Cassandra API.
    Location Select the region closest to your users Select a geographic location to host your Azure Cosmos DB account. Use the location that's closest to your users to give them the fastest access to the data.
    Capacity mode Provisioned throughput or Serverless Select Provisioned throughput to create an account in provisioned throughput mode. Select Serverless to create an account in serverless mode.

    Select Review+Create. You can skip the Networking, Backup, Encryption and Tags section.

    The new account page for Azure Cosmos DB

  5. The account creation takes a few minutes. Wait for the portal to display the page saying Congratulations! Your Azure Cosmos DB account was created.

Clone the sample application

Start by cloning the application from GitHub.

  1. Open a command prompt and create a new folder named git-samples.

    md "C:\git-samples"
    
  2. Open a git terminal window, such as git bash. Use the cd command to change into the new folder and install the sample app.

    cd "C:\git-samples"
    
  3. Run the following command to clone the sample repository. This command creates a copy of the sample app on your computer.

    git clone https://github.com/Azure-Samples/azure-cosmos-db-cassandra-go-getting-started.git
    

Review the code

This step is optional. If you're interested to learn how the code creates the database resources, you can review the following code snippets. Otherwise, you can skip ahead to Run the application

The GetSession function (part of utils\utils.go) returns a *gocql.Session that is used to execute cluster operations such as insert, find etc.

func GetSession(cosmosCassandraContactPoint, cosmosCassandraPort, cosmosCassandraUser, cosmosCassandraPassword string) *gocql.Session {
    clusterConfig := gocql.NewCluster(cosmosCassandraContactPoint)
    port, err := strconv.Atoi(cosmosCassandraPort)
    
    clusterConfig.Authenticator = gocql.PasswordAuthenticator{Username: cosmosCassandraUser, Password: cosmosCassandraPassword}
    clusterConfig.Port = port
    clusterConfig.SslOpts = &gocql.SslOptions{Config: &tls.Config{MinVersion: tls.VersionTLS12}}
    clusterConfig.ProtoVersion = 4
    
    session, err := clusterConfig.CreateSession()
    ...
    return session
}

The Azure Cosmos DB Cassandra host is passed to the gocql.NewCluster function to get a *gocql.ClusterConfig struct that is then configured to use the username, password, port, and appropriate TLS version (HTTPS/SSL/TLS encryption Security requirement)

The GetSession function is then called from the main function (main.go).

func main() {
    session := utils.GetSession(cosmosCassandraContactPoint, cosmosCassandraPort, cosmosCassandraUser, cosmosCassandraPassword)
    defer session.Close()
    ...
}

The connectivity information and credentials are accepted in the form of environment variables (resolved in the init method)

func init() {
    cosmosCassandraContactPoint = os.Getenv("COSMOSDB_CASSANDRA_CONTACT_POINT")
    cosmosCassandraPort = os.Getenv("COSMOSDB_CASSANDRA_PORT")
    cosmosCassandraUser = os.Getenv("COSMOSDB_CASSANDRA_USER")
    cosmosCassandraPassword = os.Getenv("COSMOSDB_CASSANDRA_PASSWORD")

    if cosmosCassandraContactPoint == "" || cosmosCassandraUser == "" || cosmosCassandraPassword == "" {
        log.Fatal("missing mandatory environment variables")
    }
}

It is then used to execute various operations (part of operations\setup.go) on Azure Cosmos DB starting with keyspace and table creation.

As the name suggests, the DropKeySpaceIfExists function drops the keyspace only if it exists.

const dropKeyspace = "DROP KEYSPACE IF EXISTS %s"

func DropKeySpaceIfExists(keyspace string, session *gocql.Session) {
    err := utils.ExecuteQuery(fmt.Sprintf(dropKeyspace, keyspace), session)
    if err != nil {
        log.Fatal("Failed to drop keyspace", err)
    }
    log.Println("Keyspace dropped")
}

CreateKeySpace function is used to create the keyspace (user_profile)

const createKeyspace = "CREATE KEYSPACE %s WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'datacenter1' : 1 }"

func CreateKeySpace(keyspace string, session *gocql.Session) {
    err := utils.ExecuteQuery(fmt.Sprintf(createKeyspace, keyspace), session)
    if err != nil {
        log.Fatal("Failed to create keyspace", err)
    }
    log.Println("Keyspace created")
}

This is followed by table creation (user) which is taken care of CreateUserTable function

const createTable = "CREATE TABLE %s.%s (user_id int PRIMARY KEY, user_name text, user_bcity text)"

func CreateUserTable(keyspace, table string, session *gocql.Session) {
    err := session.Query(fmt.Sprintf(createTable, keyspace, table)).Exec()
    if err != nil {
        log.Fatal("failed to create table ", err)
    }
    log.Println("Table created")
}

Once the keyspace and table are created, we invoke CRUD operations (part of operations\crud.go).

InsertUser is used to create a User. It sets the user info (ID, name, and city) as the query arguments using Bind

const createQuery = "INSERT INTO %s.%s (user_id, user_name , user_bcity) VALUES (?,?,?)"

func InsertUser(keyspace, table string, session *gocql.Session, user model.User) {
    err := session.Query(fmt.Sprintf(createQuery, keyspace, table)).Bind(user.ID, user.Name, user.City).Exec()
    if err != nil {
        log.Fatal("Failed to create user", err)
    }
    log.Println("User created")
}

FindUser is used to search for a user (model\user.go) using a specific user ID while Scan binds the user attributes (returned by Cassandra) to individual variables (userid, name, city) -it is just one of the ways in which you can use the result obtained as the search query result

const selectQuery = "SELECT * FROM %s.%s where user_id = ?"

func FindUser(keyspace, table string, id int, session *gocql.Session) model.User {
    var userid int
    var name, city string
    err := session.Query(fmt.Sprintf(selectQuery, keyspace, table)).Bind(id).Scan(&userid, &name, &city)

    if err != nil {
        if err == gocql.ErrNotFound {
            log.Printf("User with id %v does not exist\n", id)
        } else {
            log.Printf("Failed to find user with id %v - %v\n", id, err)
        }
    }
    return model.User{ID: userid, Name: name, City: city}
}

FindAllUsers is used to fetch all the users. SliceMap is used as a shorthand to get all the user's info in the form of a slice of maps. Think of each map as key-value pairs where column name (for example, user_id) is the key along with its respective value.

const findAllUsersQuery = "SELECT * FROM %s.%s"

func FindAllUsers(keyspace, table string, session *gocql.Session) []model.User {
    var users []model.User
    results, _ := session.Query(fmt.Sprintf(findAllUsersQuery, keyspace, table)).Iter().SliceMap()

    for _, u := range results {
        users = append(users, mapToUser(u))
    }
    return users
}

Each map of user info is converted to a User using mapToUser function that simply extracts the value from its respective column and uses it to create an instance of the User struct

func mapToUser(m map[string]interface{}) model.User {
    id, _ := m["user_id"].(int)
    name, _ := m["user_name"].(string)
    city, _ := m["user_bcity"].(string)

    return model.User{ID: id, Name: name, City: city}
}

Run the application

As previously mentioned, the application accepts connectivity and credentials in the form the environment variables.

  1. In your Azure Cosmos DB account in the Azure portal, select Connection String.

    View and copy details from the Connection String page in Azure portal

Copy the values for the following attributes (CONTACT POINT, PORT, USERNAME and PRIMARY PASSWORD) and set them to the respective environment variables

set COSMOSDB_CASSANDRA_CONTACT_POINT=<value for "CONTACT POINT">
set COSMOSDB_CASSANDRA_PORT=<value for "PORT">
set COSMOSDB_CASSANDRA_USER=<value for "USERNAME">
set COSMOSDB_CASSANDRA_PASSWORD=<value for "PRIMARY PASSWORD">

In the terminal window, change to the correct folder. For example:

cd "C:\git-samples\azure-cosmosdb-cassandra-go-getting-started"
  1. In the terminal, run the following command to start the application.
go run main.go
  1. The terminal window displays notifications for the various operations including keyspace and table setup, user creation etc.

  2. In the Azure portal, open Data Explorer to query, modify, and work with this new data.

    View the data in Data Explorer - Azure Cosmos DB

Review SLAs in the Azure portal

The Azure portal monitors your Cosmos DB account throughput, storage, availability, latency, and consistency. Charts for metrics associated with an Azure Cosmos DB Service Level Agreement (SLA) show the SLA value compared to actual performance. This suite of metrics makes monitoring your SLAs transparent.

To review metrics and SLAs:

  1. Select Metrics in your Cosmos DB account's navigation menu.

  2. Select a tab such as Latency, and select a timeframe on the right. Compare the Actual and SLA lines on the charts.

    Azure Cosmos DB metrics suite

  3. Review the metrics on the other tabs.

Clean up resources

When you're done with your app and Azure Cosmos DB account, you can delete the Azure resources you created so you don't incur more charges. To delete the resources:

  1. In the Azure portal Search bar, search for and select Resource groups.

  2. From the list, select the resource group you created for this quickstart.

    Select the resource group to delete

  3. On the resource group Overview page, select Delete resource group.

    Delete the resource group

  4. In the next window, enter the name of the resource group to delete, and then select Delete.

Next steps

In this quickstart, you learned how to create an Azure Cosmos DB account with Cassandra API, and run a Go app that creates a Cassandra database and container. You can now import additional data into your Azure Cosmos DB account.