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Managing Connections using the Python SDK with Couchbase Server

  • concept

    Please also refer to the Server docs.

    This section describes how to connect the Python 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

    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:

    cluster = Cluster.connect("", ClusterOptions(PasswordAuthenticator("username", "password")))
    bucket = cluster.bucket("travel-sample")
    collection = bucket.default_collection()
    # You can access multiple buckets using the same Cluster object.
    another_bucket = cluster.bucket("beer-sample")
    # You can access collections other than the default
    # if your version of Couchbase Server supports this feature.
    customer_a = bucket.scope("customer-a")
    widgets = customer_a.collection("widgets")
    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:

    cluster = Cluster.connect("couchbase://,", ClusterOptions(PasswordAuthenticator("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.

    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.

    A connection string may optionally be prefixed by either "couchbase://" or "couchbases://".

    For more detailed documentation please refer to the libcouchbase connection string documentation.

    Connection Lifecycle

    Most of the high-level classes in the Python SDK are designed to be safe for concurrent use by multiple threads. For asynchronous modes, you will get the best performance if you share and reuse instances of Cluster, Bucket, Scope, and Collection, all of which are thread-safe. For synchronous mode, it is better to use separate instances in different threads.

    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.

    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.

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

    Secure Connections

    If the client cannot load or was not built with OpenSSL, attempting an SSL connection will result in a 'FEATURE_UNAVAILABLE'.

    Couchbase Server Enterprise Edition supports 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 before proceeding with configuring encryption on the client side.

    To configure encryption for the Python SDK:

    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. Setting TLSSkipVerify is a workaround if you need to use ` couchbases://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.crt). It looks similar to this:

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

    The next step is to enable encryption by connecting to a cluster with the 'couchbases://' protocol in the connection string and pass it the path to the certificate file via an Authenticator, or via '?cert_path=…​' in the connection string itself.

    cluster = Cluster("couchbases://",ClusterOptions(PasswordAuthenticator("username","password",cert_path="/path/to/cluster.crt")))

    Then use this custom Cluster when opening the connection to the cluster.

    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..

    Working in the Cloud

    For most use cases, connecting client software using a Couchbase SDK to the new Couchbase Cloud 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 Availability Zone). 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 the Couchbase Cloud 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 APIs

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

    Methods in the asynchronous API return instances of the relevant Async API:

    1. Future for asyncio (acouchbase.bucket.Bucket supplies the relevant Bucket object)

    2. Deferred for Twisted (to be added for SDK3)

    3. For GEvent, the 'synchronous' return value is supplied to the calling greenlet code (to be added for SDK3)