4. Kea Database Administration

4.1. Databases and Database Version Numbers

Kea may be configured to use a database as a storage for leases or as a source of servers’ configurations and host reservations (i.e. static assignments of addresses, prefixes, options, etc.). Kea updates introduce changes to the database schemas to faciliate new features and correct discovered issues with the existing schemas.

A given version of Kea expects a particular structure in the backend and checks for this by examining the version of the database it is using. Separate version numbers are maintained for backends, independent of the version of Kea itself. It is possible that the backend version will stay the same through several Kea revisions; similarly, it is possible that the version of the backend may go up several revisions during a Kea upgrade. Versions for each backend are independent, so an increment in the MySQL backend version does not imply an increment in that of PostgreSQL.

Backend versions are specified in a major.minor format. The minor number is increased when there are backwards-compatible changes introduced; for example, the addition of a new index. It is desirable but not mandatory to apply such a change; running an older backend version is possible. (Although, in the example given, running without the new index may introduce a performance penalty.) On the other hand, the major number is increased when an incompatible change is introduced; for example, an extra column is added to a table. If Kea is run on a backend that is too old (as signified by a mismatched backend major version number), Kea will refuse to run; administrative action will be required to upgrade the backend.

4.2. The kea-admin Tool

To manage the databases, Kea provides the kea-admin tool. It is able to initialize a new backend, check its version number, perform a backend upgrade, and dump lease data to a text file.

kea-admin takes two mandatory parameters: command and backend. Additional, non-mandatory options may be specified. The currently supported commands are:

  • db-init — Initializes a new database schema. This is useful during a new Kea installation. The database is initialized to the latest version supported by the version of the software being installed.
  • db-version — Reports the database backend version number. This is not necessarily equal to the Kea version number as each backend has its own versioning scheme.
  • db-upgrade — Conducts a database schema upgrade. This is useful when upgrading Kea.
  • lease-dump — Dumps the contents of the lease database (for MySQL, PostgreSQL, or CQL backends) to a CSV (comma-separated values) text file. The first line of the file contains the column names. This is meant to be used as a diagnostic tool, so it provides a portable, human-readable form of the lease data.

Note

In previous versions of Kea earlier than 1.6.0 db-init, db-version and db-upgrade commands were named lease-init, lease-version and lease-upgrade.

backend specifies the type of backend database. The currently supported types are:

  • memfile — Lease information is stored on disk in a text file.
  • mysql — Information is stored in a MySQL relational database.
  • pgsql — Information is stored in a PostgreSQL relational database.
  • cql — Information is stored in an Apache Cassandra database.

Additional parameters may be needed, depending on the setup and specific operation: username, password, and database name or the directory where specific files are located. See the appropriate manual page for details (man 8 kea-admin).

4.3. Supported Backends

The following table presents the capabilities of available backends. Please refer to the specific sections dedicated to each backend to better understand their capabilities and limitations. Choosing the right backend may be essential for the success of the deployment.

List of available backends
Feature Memfile MySQL PostgreSQL CQL (Cassandra)
Status Stable Stable Stable Experimental
Data format CSV file SQL RMDB SQL RMDB NoSQL database (Cassandra)
Leases yes yes yes yes
Host Reservations no yes yes yes
Options defined on per host basis no yes yes yes
Configuration Backend no yes no no

4.3.1. Memfile

The memfile backend is able to store lease information, but cannot store host reservation details; these must be stored in the configuration file. (There are no plans to add a host reservations storage capability to this backend.)

No special initialization steps are necessary for the memfile backend. During the first run, both kea-dhcp4 and kea-dhcp6 will create an empty lease file if one is not present. Necessary disk-write permission is required.

4.3.1.1. Upgrading Memfile Lease Files from an Earlier Version of Kea

There are no special steps required to upgrade memfile lease files from an earlier version of Kea to a new version of Kea. During startup the servers will check the schema version of the lease files against their own. If there is a mismatch, the servers will automatically launch the LFC process to convert the files to the server’s schema version. While this mechanism is primarily meant to ease the process of upgrading to newer versions of Kea, it can also be used for downgrading should the need arise. When upgrading, any values not present in the original lease files will be assigned appropriate default values. When downgrading, any data present in the files but not in the server’s schema will be dropped. To convert the files manually prior to starting the servers, run the LFC process. See The LFC Process for more information.

4.3.2. MySQL

MySQL is able to store leases, host reservations, options defined on a per-host basis, and a subset of the server configuration parameters (serving as a configuration backend). This section can be safely ignored if the data will be stored in other backends.

4.3.2.1. First-Time Creation of the MySQL Database

When setting up the MySQL database for the first time, the database area must be created within MySQL, and the MySQL user ID under which Kea will access the database must be set up. This needs to be done manually, rather than via kea-admin.

To create the database:

  1. Log into MySQL as “root”:

    $ mysql -u root -p
    Enter password:
    mysql>
    
  2. Create the MySQL database:

    mysql> CREATE DATABASE database_name;
    

    (database_name is the name chosen for the database.)

  3. Create the user under which Kea will access the database (and give it a password), then grant it access to the database tables:

    mysql> CREATE USER 'user-name'@'localhost' IDENTIFIED BY 'password';
    mysql> GRANT ALL ON database-name.* TO 'user-name'@'localhost';
    

    (user-name and password are the user ID and password being used to allow Kea access to the MySQL instance. All apostrophes in the command lines above are required.)

  4. At this point, administrators may elect to create the database tables. (Alternatively, the tables can be created by exiting MySQL and using the kea-admin tool, as explained below.) To do this:

    mysql> CONNECT database-name;
    mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_create.mysql
    

    (path-to-kea is the location where Kea is installed.)

  5. Exit MySQL:

    mysql> quit
    Bye
    

If the tables were not created in Step 4, run the kea-admin tool to create them now:

$ kea-admin db-init mysql -u database-user -p database-password -n database-name

Do not do this if the tables were created in Step 4. kea-admin implements rudimentary checks; it will refuse to initialize a database that contains any existing tables. To start from scratch, all must be removed data manually. (This process is a manual operation on purpose, to avoid possibly irretrievable mistakes by kea-admin.)

4.3.2.2. Upgrading a MySQL Database from an Earlier Version of Kea

Sometimes a new Kea version may use a newer database schema, so the existing database will need to be upgraded. This can be done using the kea-admin db-upgrade command.

To check the current version of the database, use the following command:

$ kea-admin db-version mysql -u database-user -p database-password -n database-name

(See Databases and Database Version Numbers for a discussion about versioning.) If the version does not match the minimum required for the new version of Kea (as described in the release notes), the database needs to be upgraded.

Before upgrading, please make sure that the database is backed up. The upgrade process does not discard any data, but depending on the nature of the changes, it may be impossible to subsequently downgrade to an earlier version. To perform an upgrade, issue the following command:

$ kea-admin db-upgrade mysql -u database-user -p database-password -n database-name

4.3.3. PostgreSQL

PostgreSQL is able to store leases, host reservations, and options defined on a per-host basis. This step can be safely ignored if other database backends will be used.

4.3.3.1. First-Time Creation of the PostgreSQL Database

The first task is to create both the database and the user under which the servers will access it. A number of steps are required:

  1. Log into PostgreSQL as “root”:

    $ sudo -u postgres psql postgres
    Enter password:
    postgres=#
    
  2. Create the database:

    postgres=# CREATE DATABASE database-name;
    CREATE DATABASE
    postgres=#
    

    (database-name is the name chosen for the database.)

  3. Create the user under which Kea will access the database (and give it a password), then grant it access to the database:

    postgres=# CREATE USER user-name WITH PASSWORD 'password';
    CREATE ROLE
    postgres=# GRANT ALL PRIVILEGES ON DATABASE database-name TO user-name;
    GRANT
    postgres=#
    
  4. Exit PostgreSQL:

    postgres=# \q
    Bye
    $
    
  5. At this point, create the database tables either using the kea-admin tool, as explained in the next section (recommended), or manually. To create the tables manually, enter the following command. Note that PostgreSQL will prompt the administrator to enter the new user’s password that was specified in Step 3. When the command completes, Kea will return to the shell prompt. The output should be similar to the following:

    $ psql -d database-name -U user-name -f path-to-kea/share/kea/scripts/pgsql/dhcpdb_create.pgsql
    Password for user user-name:
    CREATE TABLE
    CREATE INDEX
    CREATE INDEX
    CREATE TABLE
    CREATE INDEX
    CREATE TABLE
    START TRANSACTION
    INSERT 0 1
    INSERT 0 1
    INSERT 0 1
    COMMIT
    CREATE TABLE
    START TRANSACTION
    INSERT 0 1
    COMMIT
    $
    

    (path-to-kea is the location where Kea is installed.)

    If instead an error is encountered, such as:

    psql: FATAL:  no pg_hba.conf entry for host "[local]", user "user-name", database "database-name", SSL off
    

    … the PostgreSQL configuration will need to be altered. Kea uses password authentication when connecting to the database and must have the appropriate entries added to PostgreSQL’s pg_hba.conf file. This file is normally located in the primary data directory for the PostgreSQL server. The precise path may vary depending on the operating system and version, but the default location for PostgreSQL 9.3 on Centos 6.5 is: /var/lib/pgsql/9.3/data/pg_hba.conf.

    Assuming Kea is running on the same host as PostgreSQL, adding lines similar to the following should be sufficient to provide password-authenticated access to Kea’s database:

    local   database-name    user-name                                 password
    host    database-name    user-name          127.0.0.1/32           password
    host    database-name    user-name          ::1/128                password
    

    These edits are primarily intended as a starting point, and are not a definitive reference on PostgreSQL administration or database security. Please consult the PostgreSQL user manual before making these changes, as they may expose other databases that are running. It may be necessary to restart PostgreSQL in order for the changes to take effect.

4.3.3.2. Initialize the PostgreSQL Database Using kea-admin

If the tables were not created manually, do so now by running the kea-admin tool:

$ kea-admin db-init pgsql -u database-user -p database-password -n database-name

Do not do this if the tables were already created manually. kea-admin implements rudimentary checks; it will refuse to initialize a database that contains any existing tables. To start from scratch, all data must be removed manually. (This process is a manual operation on purpose, to avoid possibly irretrievable mistakes by kea-admin.)

4.3.3.3. Upgrading a PostgreSQL Database from an Earlier Version of Kea

The PostgreSQL database schema can be upgraded using the same tool and commands as described in Upgrading a MySQL Database from an Earlier Version of Kea, with the exception that the “pgsql” database backend type must be used in the commands.

Use the following command to check the current schema version:

$ kea-admin db-version pgsql -u database-user -p database-password -n database-name

Use the following command to perform an upgrade:

$ kea-admin db-upgrade pgsql -u database-user -p database-password -n database-name

4.3.4. Cassandra

Cassandra (sometimes for historical reasons referred to in documentation and commands as CQL) is the newest backend added to Kea; initial development was contributed by Deutsche Telekom. The Cassandra backend is able to store leases, host reservations, and options defined on a per-host basis.

Cassandra must be properly set up if Kea is to store information in it. This section can be safely ignored if the data will be stored in other backends.

4.3.4.1. First-Time Creation of the Cassandra Database

When setting up the Cassandra database for the first time, the keyspace area within it must be created. This needs to be done manually; it cannot be performed by kea-admin.

To create the database:

  1. Export CQLSH_HOST environment variable:

    $ export CQLSH_HOST=localhost
    
  2. Log into CQL:

    $ cqlsh
    cql>
    
  3. Create the CQL keyspace:

    cql> CREATE KEYSPACE keyspace-name WITH replication = {'class' : 'SimpleStrategy','replication_factor' : 1};
    

    (keyspace-name is the name chosen for the keyspace.)

  4. At this point, the database tables can be created. (It is also possible to exit Cassandra and create the tables using the kea-admin tool, as explained below.) To do this:

    cqslh -k keyspace-name -f path-to-kea/share/kea/scripts/cql/dhcpdb_create.cql
    

    (path-to-kea is the location where Kea is installed.)

If the tables were not created in Step 4, do so now by running the kea-admin tool:

$ kea-admin db-init cql -n database-name

Do not do this if the tables were created in Step 4. kea-admin implements rudimentary checks; it will refuse to initialize a database that contains any existing tables. To start from scratch, all data must be removed manually. (This process is a manual operation on purpose, to avoid possibly irretrievable mistakes by kea-admin.)

4.3.4.2. Upgrading a Cassandra Database from an Earlier Version of Kea

Sometimes a new Kea version may use a newer database schema, so the existing database will need to be upgraded. This can be done using the kea-admin db-upgrade command.

To check the current version of the database, use the following command:

$ kea-admin db-version cql -n database-name

(See Databases and Database Version Numbers for a discussion about versioning.) If the version does not match the minimum required for the new version of Kea (as described in the release notes), the database needs to be upgraded.

Before upgrading, please make sure that the database is backed up. The upgrade process does not discard any data, but depending on the nature of the changes, it may be impossible to subsequently downgrade to an earlier version. To perform an upgrade, issue the following command:

$ kea-admin db-upgrade cql -n database-name

4.3.5. Using Read-Only Databases with Host Reservations

If a read-only database is used for storing host reservations, Kea must be explicitly configured to operate on the database in read-only mode. Sections Using Read-Only Databases for Host Reservations with DHCPv4 and Using Read-Only Databases for Host Reservations with DHCPv6 describe when such a configuration may be required, and how to configure Kea to operate in this way for both DHCPv4 and DHCPv6.