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

APPLIES TO: Cassandra

• .NET
• .NET Core
• Java v3
• Java v4
• Node.js
• Python
• Golang

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 for Apache Cassandra 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

• An Azure account with an active subscription. Create one for free. Or try Azure Cosmos DB for free without an Azure subscription.
• Go installed on your computer, and a working knowledge of Go.
• Git.

Create a database account

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

1. From the Azure portal menu or the Home page, select Create a resource.

2. On the New page, search for and select Azure Cosmos DB.

3. On the Azure Cosmos DB page, select Create.

4. On the API page, select Create under the Cassandra section.

   The API determines the type of account to create. Azure Cosmos DB provides five APIs: NoSQL 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 API for Cassandra.

   Learn more about the API for Cassandra.

5. In the Create Azure Cosmos DB Account page, enter the basic 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 DB 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.
   Location	The region closest to your users	Select a geographic location to host your Azure Cosmos DB account. Use the location that is 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.
   Apply Azure Cosmos DB free tier discount	Apply or Do not apply	With Azure Cosmos DB free tier, you will get the first 1000 RU/s and 25 GB of storage for free in an account. Learn more about free tier.
   Limit total account throughput	Select to limit throughput of the account	This is useful if you want to limit the total throughput of the account to a specific value.

   Note

   You can have up to one free tier Azure Cosmos DB account per Azure subscription and must opt-in when creating the account. If you do not see the option to apply the free tier discount, this means another account in the subscription has already been enabled with free tier.

   

6. In the Global Distribution tab, configure the following details. You can leave the default values for the purpose of this quickstart:

   Setting	Value	Description
   Geo-Redundancy	Disable	Enable or disable global distribution on your account by pairing your region with a pair region. You can add more regions to your account later.
   Multi-region Writes	Disable	Multi-region writes capability allows you to take advantage of the provisioned throughput for your databases and containers across the globe.
   Availability Zones	Disable	Availability Zones are isolated locations within an Azure region. Each zone is made up of one or more datacenters equipped with independent power, cooling, and networking.

   Note

   The following options are not available if you select Serverless as the Capacity mode:

   • Apply Free Tier Discount
   • Geo-redundancy
   • Multi-region Writes

7. Optionally you can configure additional details in the following tabs:

   • Networking - Configure access from a virtual network.
   • Backup Policy - Configure either periodic or continuous backup policy.
   • Encryption - Use either service-managed key or a customer-managed key.
   • Tags - Tags are name/value pairs that enable you to categorize resources and view consolidated billing by applying the same tag to multiple resources and resource groups.

8. Select Review + create.

9. Review the account settings, and then select Create. It takes a few minutes to create the account. Wait for the portal page to display Your deployment is complete.

   

10. Select Go to resource to go to the Azure Cosmos DB account page.

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.

   

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"

2. In the terminal, run the following command to start the application.

go run main.go

3. The terminal window displays notifications for the various operations including keyspace and table setup, user creation etc.

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

   

Review SLAs in the Azure portal

The Azure portal monitors your Azure 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 Azure 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.

   

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.

   

3. On the resource group Overview page, select Delete 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 API for Cassandra, and run a Go app that creates a Cassandra database and container. You can now import additional data into your Azure Cosmos DB account.

Import Cassandra data into Azure Cosmos DB