Connect to CrateDB

Note

This page documents the CrateDB Database API client.

For help using the SQLAlchemy dialect, consult the SQLAlchemy dialect documentation.

See also

Supplementary information about the CrateDB Database API client can be found in the data types appendix and the compatibility notes.

For general help using the Database API, consult PEP 0249.

Table of contents

Connect to a single node

To connect to a single CrateDB node, use the connect() function, like so:

>>> connection = client.connect("<NODE_URL>", username="<USERNAME>")

Here, replace <NODE_URL> with a URL pointing to the HTTP endpoint of a CrateDB node. Replace <USERNAME> with the username you are authenticating as.

Note

This example authenticates as crate, the default database user in CrateDB versions 2.1.x and later. This might not work for you.

Consult the Authentication section for more information.

Example node URLs:

  • http://localhost:4200/

  • http://crate-1.vm.example.com:4200/

  • http://198.51.100.1:4200/

If the CrateDB hostname is crate-1.vm.example.com and CrateDB is listening for HTTP requests on port 4200, the node URL would be http://crate-1.vm.example.com:4200/.

Tip

If a <NODE_URL> argument is not provided, the library will attempt to connect to CrateDB on the local host with the default HTTP port number, i.e. http://localhost:4200/.

If you’re just getting started with CrateDB, the first time you connect, you can probably omit this argument.

Connect to multiple nodes

To connect to one of multiple nodes, pass a list of database URLs to the connect() function, like so:

>>> connection = client.connect(["<NODE_1_URL>", "<NODE_2_URL>"], ...)

Here, <NODE_1_URL> and <NODE_2_URL> correspond to two node URLs, as described in the previous section.

You can pass in as many node URLs as you like.

Tip

For every query, the client will attempt to connect to each node in sequence until a successful connection is made. Nodes are moved to the end of the list each time they are tried.

Over multiple query executions, this behaviour functions as client-side round-robin load balancing. (This is analogous to round-robin DNS.)

Connection options

HTTPS

You can connect to a CrateDB client via HTTPS by specifying https in the URL:

>>> connection = client.connect('https://localhost:4200/', ...)

See also

The CrateDB reference has a section on setting up SSL. This will be a useful background reading for the following two subsections.

Server verification

Server certificates are verified by default. In order to connect to a SSL-enabled host using self-signed certificates, you will need to provide the CA certificate file used to sign the server SSL certificate:

>>> connection = client.connect(..., ca_cert="<CA_CERT_FILE>")

Here, replace <CA_CERT_FILE> with the path to the CA certificate file.

You can disable server SSL certificate verification by using the verify_ssl_cert keyword argument and setting it to False:

>>> connection = client.connect(..., verify_ssl_cert=False)

Client verification

The client also supports client verification via client certificates.

Here’s how you might do that:

>>> connection = client.connect(..., cert_file="<CERT_FILE>", key_file="<KEY_FILE>")

Here, replace <CERT_FILE> with the path to the client certificate file, and <KEY_FILE> with the path to the client private key file.

Tip

Often, you will want to perform server verification and client verification. In such circumstances, you can combine the two methods above to do both at once.

Timeout

Connection timeouts (in seconds) can be configured with the optional timeout argument:

>>> connection = client.connect(..., timeout=5)

Here, replace ... with the rest of your arguments.

Note

If no timeout is specified, the client will use the default Python socket timeout.

Tracebacks

Tracebacks in the event of a connection error will be printed if you set the optional error_trace argument to True, like so:

>>> connection = client.connect(..., error_trace=True)

Backoff Factor

When attempting to make a request, the connection can be configured so that retries are made in increasing time intervals. This can be configured like so:

>>> connection = client.connect(..., backoff_factor=0.1)

If backoff_factor is set to 0.1, then the delay between retries will be 0.0, 0.1, 0.2, 0.4 etc. The maximum backoff factor cannot exceed 120 seconds and by default its value is 0.

Socket Options

Creating connections uses urllib3 default socket options but additionally enables TCP keepalive by setting socket.SO_KEEPALIVE to 1.

Keepalive can be disabled using the socket_keepalive argument, like so:

>>> connection = client.connect(..., socket_keepalive=False)

If keepalive is enabled (default), there are three additional, optional socket options that can be configured via connection arguments.

socket_tcp_keepidle

Set the TCP_KEEPIDLE socket option, which overrides net.ipv4.tcp_keepalive_time kernel setting if socket_keepalive is True.

socket_tcp_keepintvl

Set the TCP_KEEPINTVL socket option, which overrides net.ipv4.tcp_keepalive_intvl kernel setting if socket_keepalive is True.

socket_tcp_keepcnt

Set the TCP_KEEPCNT socket option, which overrides net.ipv4.tcp_keepalive_probes kernel setting if socket_keepalive is True.

Authentication

Note

Authentication was introduced in CrateDB versions 2.1.x.

If you are using CrateDB 2.1.x or later, you must supply a username. If you are using earlier versions of CrateDB, this argument is not supported.

See the compatibility notes for more information.

You can authenticate with CrateDB like so:

>>> connection = client.connect(..., username="<USERNAME>", password="<PASSWORD>")

Here, replace <USERNAME> and <PASSWORD> with the appropriate username and password.

Tip

If you have not configured a custom database user, you probably want to authenticate as the CrateDB superuser, which is crate. The superuser does not have a password, so you can omit the password argument.

Schema selection

You can select a schema using the optional schema argument, like so:

>>> connection = client.connect(..., schema="<SCHEMA>")

Here, replace <SCHEMA> with the name of your schema, and replace ... with the rest of your arguments.

Tip

The default CrateDB schema is doc, and if you do not specify a schema, this is what will be used.

However, you can query any schema you like by specifying it in the query.

Next steps

Once you’re connected, you can query CrateDB.

See also

Check out the sample application (and the corresponding documentation) for a practical demonstration of this driver in use.

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