Managing Connections

  • concept
    This section describes how to connect the Scala SDK to a Couchbase cluster. It contains best practices as well as information on TLS/SSL and other advanced connection options.

    Connecting to a Cluster

    The examples below use these imports:

    import com.couchbase.client.scala._
    import com.couchbase.client.scala.env._
    import com.couchbase.client.scala.kv.GetResult
    import reactor.core.scala.publisher.SMono
    import java.nio.file.Path
    import scala.concurrent.Future
    import scala.concurrent.duration._
    import scala.util.{Failure, Success, Try}

    A connection to a Couchbase Server cluster is represented by a Cluster object. A Cluster provides access to Buckets, Scopes, and Collections, as well as various Couchbase services and management interfaces. The simplest way to create a Cluster object is to call Cluster.connect() with a connection string, username, and password:

    val clusterTry: Try[Cluster] =
      Cluster.connect("", "username", "password")
    clusterTry match {
      case Success(cluster) =>
        val bucket = cluster.bucket("beer-sample")
        val customerA = bucket.scope("customer-a")
        val widgets = customerA.collection("widgets")
      case Failure(err) =>
        println(s"Failed to open cluster: $err")
    If you are connecting to a version of Couchbase Server older than 6.5, it will be more efficient if the addresses are those of data (KV) nodes. You will in any case, with 6.0 and earlier, need to open a Bucket instance before connecting to any other HTTP services (such as Query or Search).

    In a production environment, your connection string should include the addresses of multiple server nodes in case some are currently unavailable. Multiple addresses may be specified in a connection string by delimiting them with commas:

    val connectionString = ","
    val cluster = Cluster.connect(connectionString, "username", "password")
    You don’t need to include the address of every node in the cluster. The client fetches the full address list from the first node it is able to contact.


    Opening resources is asynchronous. That is, the call to cluster.bucket or Cluster.connect will complete instantly, and opening that resource will continue in the background.

    You can force waiting for the resource to be opened with a call to waitUntilReady, which is available on both the Cluster and Bucket. Here is an example of using it on the bucket:

    val clusterTry: Try[Cluster] =
      Cluster.connect("", "username", "password")
    clusterTry match {
      case Success(cluster) =>
        val bucket = cluster.bucket("beer-sample")
        bucket.waitUntilReady(30.seconds) match {
          case Success(_) =>
            val collection = bucket.defaultCollection
            // ... continue to use collection as normal ...
          case Failure(err) =>
            println(s"Failed to open bucket: $err")
      case Failure(err) =>
        println(s"Failed to open cluster: $err")

    If not present, then the first Key Value (KV) operation on the bucket will wait for it to be ready. Any issues opening that bucket (for instance, if it does not exist), will result in an error being raised from that KV operation.

    Cluster Environment

    A ClusterEnvironment manages shared resources like thread pools, timers, and schedulers. It also holds the client settings. One way to customize the client’s behavior is to build your own ClusterEnvironment with custom settings:

    val envTry: Try[ClusterEnvironment] = ClusterEnvironment.builder
    envTry match {
      case Success(env) =>
        val clusterTry = Cluster.connect(
            .create("username", "password")
        clusterTry match {
          case Success(cluster) =>
            // ... use the Cluster
            // Shutdown gracefully by shutting down the environment after
            // any Clusters using it
          case Failure(err) => println(s"Failed to open cluster: $err")
      case Failure(err) => println(s"Failed to create environment: $err")

    This is a verbose example for simplicity, and the user may prefer to use flatMap or a for-comprehension to combine the multiple Try.

    Note there are com.couchbase.client.scala.env and com.couchbase.client.core.env versions of all environment parameters: be sure to import the .scala versions.

    If you create a Cluster without specifying a custom environment, the client creates a default environment used exclusively by that Cluster. This default ClusterEnvironment is managed completely by the Scala SDK, and is automatically shut down when the associated Cluster is disconnected.

    Connection Strings

    A Couchbase connection string is a comma-delimited list of IP addresses and/or hostnames, optionally followed by a list of parameters.

    The parameter list is just like the query component of a URI; name-value pairs have an equals sign (=) separating the name and value, with an ampersand (&) between each pair. Just as in a URI, the first parameter is prefixed by a question mark (?).

    Simple connection string with one seed node
    Connection string with two seed nodes,
    Connection string with two parameters

    The full list of recognized parameters is documented in the client settings reference. Any client setting with a system property name may also be specified as a connection string parameter (without the com.couchbase.env. prefix).

    When creating a Cluster using a custom ClusterEnvironment, connection string parameters are ignored, since client settings are frozen when the cluster environment is built.

    Connection Lifecycle

    Most of the high-level classes in the Scala SDK are designed to be safe for concurrent use by multiple threads. You will get the best performance if you share and reuse instances of ClusterEnvironment, Cluster, Bucket, Scope, and Collection, all of which are thread-safe.

    We recommend creating a single Cluster instance when your application starts up, and sharing this instance throughout your application. If you know at startup time which buckets, scopes, and collections your application will use, we recommend obtaining them from the Cluster at startup time and sharing those instances throughout your application as well.

    Before your application stops, gracefully shut down the client by calling the disconnect() method of each Cluster you created. If you created any ClusterEnvironment instances, call their shutdown() method after disconnecting the associated clusters.

    Connecting to Multiple Clusters

    If a single application needs to connect to multiple Couchbase Server clusters, we recommend creating a single ClusterEnvironment and sharing it between the Clusters. We will use a for-comprehension here to avoid excessive Try juggling.

    val result = for {
      env <- ClusterEnvironment.builder
      clusterA <- Cluster.connect(
          .create("username", "password")
      clusterB <- Cluster.connect(
          .create("username", "password")
      result <- doSomethingWithClusters(clusterA, clusterB)
      _ <- Success(clusterA.disconnect())
      _ <- Success(clusterB.disconnect())
      _ <- Success(env.shutdown())
    } yield result
    result match {
      case Failure(err) => println(s"Failure: $err")
      case _            =>

    Remember, whenever you manually create a ClusterEnvironment like this, the SDK will not shut it down when you call Cluster.disconnect(). Instead you are responsible for shutting it down after disconnecting all clusters that share the environment.

    Alternate Addresses and Custom Ports

    If your Couchbase Server cluster is running in a containerized, port mapped, or otherwise NAT’d environment like Docker or Kubernetes, a client running outside that environment may need additional information in order to connect the cluster. Both the client and server require special configuration in this case.

    On the server side, each server node must be configured to advertise its external address as well as any custom port mapping. This is done with the setting-alternate-address CLI command introduced in Couchbase Server 6.5. A node configured in this way will advertise two addresses: one for connecting from the same network, and another for connecting from an external network.

    On the client side, the externally visible ports must be used when connecting. If the external ports are not the default, you can specify custom ports using the overloaded Cluster.connect() method that takes a set of SeedNode objects instead of a connection string.

    val customKvPort = 1234
    val customManagerPort = 2345
    val seedNodes = Set(
      SeedNode("", Some(customKvPort), Some(customManagerPort))
    val cluster = Cluster.connect(seedNodes, ClusterOptions.create("username", "password"))
    In a deployment that uses multi-dimensional scaling, a custom KV port is only applicable for nodes running the KV service. A custom manager port may be specified regardless of which services are running on the node.

    In many cases the client is able to automatically select the correct set of addresses to use when connecting to a cluster that advertises multiple addresses. If the detection heuristic fails in your environment, you can override it by setting the io.networkResolution client setting to default if the client and server are on the same network, or external if they’re on different networks.

    Any TLS certificates must be set up at the point where the connections are being made.

    Secure Connections

    Couchbase Server Enterprise Edition and Couchbase Capella support full encryption of client-side traffic using Transport Layer Security (TLS). That includes key-value type operations, queries, and configuration communication. Make sure you have the Enterprise Edition of Couchbase Server, or a Couchbase Capella account, before proceeding with configuring encryption on the client side.

    • Couchbase Capella

    • Couchbase Server

    The Scala SDK bundles Capella’s standard root certificate by default. This means you don’t need any additional configuration to enable TLS — simply use couchbases:// in your connection string.

    Capella’s root certificate is not signed by a well known CA (Certificate Authority). However, as the certificate is bundled with the SDK, it is trusted by default.

    As of SDK 1.4, if you connect to a Couchbase Server cluster with a root certificate issued by a trusted CA (Certificate Authority), you no longer need to configure this in the securityConfig settings.

    The cluster’s root certificate just needs to be issued by a CA whose certificate is in the JVM’s trust store. This includes well known CAs (e.g., GoDaddy, Verisign, etc…​), plus any other CA certificates that you wish to add.

    The JVM’s trust store is represented by a file named cacerts, which can be found inside your Java installation folder.

    You can still provide a certificate explicitly if necessary:

    1. Get the CA certificate from the cluster and save it in a text file.

    2. Enable encryption on the client side and point it to the file containing the certificate.

    It is important to make sure you are transferring the certificate in an encrypted manner from the server to the client side, so either copy it through SSH or through a similar secure mechanism.

    If you are running on localhost and just want to enable TLS for a development machine, just copying and pasting it suffices — so long as you use rather than localhost in the connection string. This is because the certificate will not match the name localhost.

    Navigate in the admin UI to Settings  Cluster and copy the input box of the TLS certificate into a file on your machine (which we will refer to as cluster.cert). It looks similar to this:

    -----END CERTIFICATE-----

    The next step is to enable encryption and pass it the path to the certificate file.

    val env = ClusterEnvironment.builder

    Then use this custom ClusterEnvironment when opening the connection to the cluster. See Cluster Environment for an example of creating a Cluster with a custom environment.

    If you want to verify it’s actually working, you can use a tool like tcpdump. For example, an unencrypted upsert request looks like this (using sudo tcpdump -i lo0 -A -s 0 port 11210):


    After enabling encryption, you cannot inspect the traffic in cleartext (same upsert request, but watched on port 11207 which is the default encrypted port):

    ..... ...xuG.O=.#.........?.Q)8..D...S.W.4.-#....@7...^.Gk.4.t..C+......6..)}......N..m..o.3...d.,.	...W.....U..

    Cloud Native Gateway

    Couchbase’s next generation connection protocol, introduced in Scala SDK 1.5 and Couchbase Autonomous Operator 2.6.1, can be enabled simply by changing the connection string to couchbase2:// but there are a few differences to be aware of, described below.

    The protocol implements a gRPC-style interface between the SDK and Couchbase Server (in this case, only available in the Server running on Kubernetes or OpenShift, with a forthcoming release of Couchbase Autonomous Operator.


    The underlying protocol will not work with certain legacy features: MapReduce Views (a deprecated Service — use Query instead) and Memcached buckets (superseded by the improved Ephemeral Buckets).

    The following are not currently implemented over the couchbase2:// protocol:

    • Authentication by client certificate.

    • Multi-document ACID transactions.

    • Analytics service.

    • Health Check.

    There are some different behaviors seen with this protocol:

    • Some config options are unsupported — see the Settings page.

    • The SDK will poll the gRPC channels until they are in a good state, or return an error, or timeout while waiting — in our standard protocol there is an option of setting waitUntilReady() for just certain services to become available.

    • Some error codes are more generic — in cases where the client would not be expected to need to take specific action — but should cause no problem, unless you have written code looking at individual strings within the error messages.

    • Although documents continue to be stored compressed by Couchbase Server, they will not be transmitted in compressed form (to and from the client) over the wire, using couchbase2://.

    Working in the Cloud

    For most use cases, connecting client software using a Couchbase SDK to the Couchbase Capella service is similar to connecting to an on-premises Couchbase Cluster. The use of DNS-SRV, Alternate Address, and TLS is covered above.

    We strongly recommend that the client and server are in the same LAN-like environment (e.g. AWS Region). As this may not always be possible during development, read the guidance on working with constrained network environments. More details on connecting your client code to Couchbase Capella can be found in the Cloud docs.

    Troubleshooting Connections to Cloud

    Some DNS caching providers (notably, home routers) can’t handle an SRV record that’s large — if you have DNS-SRV issues with such a set-up, reduce your DNS-SRV to only include three records. [For development only, not production.]. Our Troubleshooting Cloud Connections page will help you to diagnose this and other problems — as well as introducing the SDK doctor tool.

    Async and Reactive APIs

    The Couchbase Scala SDK provides first-class support for asynchronous and reactive programming. In fact, the synchronous API is just a thin wrapper around the asynchronous API.

    Methods in the asynchronous API return instances of the standard Scala Future.

    The Scala SDK’s reactive API is built on Project Reactor and the Scala extensions. Reactor implements the standard Reactive Streams API introduced in Scala 9, and extends it with a rich set of useful operators. Methods in the reactive API return instances of SFlux or SMono.

    If you wish to embrace the async or reactive programming model, there are two ways to get started:

    • Call async or reactive on the object to access its Async* or Reactive* counterpart. For example, if you have a Collection called myCollection, you can obtain a ReactiveCollection by calling myCollection.reactive.

    • Instantiate an AsyncCluster or ReactiveCluster in the first place. The bucket() method of an AsyncCluster returns an AsyncBucket, while the bucket() method of a ReactiveCluster turns a ReactiveBucket.

    So if you are connecting to the bucket synchronously but then want to switch over to asynchronous data operations, you can do it like this:

    Cluster.connect("", "username", "password") match {
      case Success(cluster: Cluster) =>
        val bucket: Bucket = cluster.bucket("travel-sample")
        val async: AsyncBucket = bucket.async
        val reactive: ReactiveBucket = bucket.reactive
        val r1: Try[GetResult] = bucket.defaultCollection.get("id")
        val r2: Future[GetResult] = async.defaultCollection.get("id")
        val r3: SMono[GetResult] = reactive.defaultCollection.get("id")
      case Failure(err) => println(s"Failure: $err")

    On the other hand, you can use the Async API right from the beginning:

    AsyncCluster.connect("", "username", "password") match {
      case Success(cluster: AsyncCluster) =>
        val async: AsyncBucket = cluster.bucket("travel-sample")
      case Failure(err) => println(s"Failure: $err")

    Here’s the same example, but using the Reactive API instead of the Async API:

    ReactiveCluster.connect("", "username", "password") match {
      case Success(cluster: ReactiveCluster) =>
        val async: ReactiveBucket = cluster.bucket("travel-sample")
      case Failure(err) => println(s"Failure: $err")