4. Kea Database Administration

4.1. Databases and Schema Versions

Kea may be configured to use a database as storage for leases or as a source of servers' configurations and host reservations (i.e. static assignments of addresses, prefixes, options, etc.). As Kea is updated, new database schemas are introduced to facilitate new features and correct discovered issues with the existing schemas.

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

Schema versions are specified in a major.minor format. For the most recent versions, the minor version is always zero and only the major version is incremented.

Historically, the minor version used to be incremented when backward-compatible changes were introduced to the schema: for example - when a new index is added. This was opposed to incrementing the major version which implied an incompatible schema change: for example - changing the type of an existing column. If Kea attempts to run on a schema that is too old, as indicated by a mismatched schema version, it will fail; administrative action is required to upgrade the schema.

4.2. The kea-admin Tool

To manage the databases, Kea provides the kea-admin tool. It can 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, which is useful during a new Kea installation. The new database is updated to match the Kea version being installed. kea-admin is automatically invoked with this command if a missing schema is detected during startup or reconfiguration of Kea DHCP servers.

• 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 or PostgreSQL backends) to a CSV (comma-separated values) text file.

  The first line of the file contains the column names. This can be used as a way to switch from a database backend to a memfile backend. Alternatively, it can be used as a diagnostic tool, so it provides a portable form of the lease data.

• lease-upload — uploads leases from a CSV (comma-separated values) text file to a MySQL or a PostgreSQL lease database. The CSV file needs to be in memfile format.

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.

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 is essential for the success of the deployment.

List of available backends

Feature	Memfile	MySQL	PostgreSQL
Status	Stable	Stable	Stable
Data format	CSV file	SQL RMDB	SQL RMDB
Leases	yes	yes	yes
Host reservations	no	yes	yes
Options defined on per host basis	no	yes	yes
Configuration backend	no	yes	yes

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 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 between versions of Kea. During startup, the servers check the schema version of the lease files against their own. If there is a mismatch, the servers 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 are assigned appropriate default values. When downgrading, any data present in the files but not in the server's schema are dropped. To convert the files manually prior to starting the servers, run the lease file cleanup (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).

4.3.2.1. MySQL 5.7 vs MySQL 8 vs MariaDB 10 and 11

In our Kea performance testing, MySQL 8 shows a 60-90% drop in speed in comparison with MySQL 5.7. Due to the upcoming MySQL 5.7 EOL, we recommend using MariaDB instead of MySQL 8.

MySQL 5.7, MySQL 8, MariaDB 10, and MariaDB 11 are fully compatible, interchangeable, and tested with Kea.

4.3.2.2. First-Time Creation of the MySQL Database

Before preparing any Kea-specific database and tables, the MySQL database must be configured to use the system timezone. It is recommended to use UTC as the timezone for both the system and the MySQL database.

To check the system timezone:

date +%Z

To check the MySQL timezone:

mysql> SELECT @@system_time_zone;
mysql> SELECT @@global.time_zone;
mysql> SELECT @@session.time_zone;

To configure the MySQL timezone for a specific server, please refer to the installed version documentation.

Usually the setting is configured in the [mysqld] section in /etc/mysql/my.cnf, /etc/mysql/mysql.cnf, /etc/mysql/mysqld.cnf, or /etc/mysql/mysql.conf.d/mysqld.cnf.

[mysqld]
# using default-time-zone
default-time-zone='+00:00'

# or using timezone
timezone='UTC'

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 used to allow Kea access to the MySQL instance. All apostrophes in the command lines above are required.)

4. Create the database.

   Exit the MySQL client

   mysql> quit
   Bye
   

   Then use the kea-admin tool to create the database.

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

   While it is possible to create the database from within the MySQL client, we recommend using the kea-admin tool as it performs some necessary validations to ensure Kea can access the database at runtime. Among those checks is verification that the schema does not contain any pre-existing tables; any pre-existing tables must be removed manually. An additional check examines the user's ability to create functions and triggers. The following error indicates that the user does not have the necessary permissions to create functions or triggers:

   ERROR 1419 (HY000) at line 1: You do not have the SUPER privilege and binary logging is
   enabled (you *might* want to use the less safe log_bin_trust_function_creators variable)
   ERROR/kea-admin: mysql_can_create cannot trigger, check user permissions, mysql status = 1
   mysql: [Warning] Using a password on the command line interface can be insecure.
   ERROR/kea-admin: Create failed, the user, keatest, has insufficient privileges.
   

   The simplest way around this is to set the global MySQL variable, log_bin_trust_function_creators, to 1 via the MySQL client. Note this must be done as a user with SUPER privileges:

   mysql> set @@global.log_bin_trust_function_creators = 1;
   Query OK, 0 rows affected (0.00 sec)
   

   To create the database with MySQL directly, follow these steps:

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

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

   The database may also be dropped manually as follows:

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

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

Warning

Dropping the database results in the unrecoverable loss of any data it contains.

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 data must be removed manually. (This process is a manual operation on purpose, to avoid accidentally irretrievable mistakes by kea-admin.)

4.3.2.3. Upgrading a MySQL Database From an Earlier Version of Kea

Sometimes a new Kea version uses a newer database schema, so the existing database needs 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 Schema Versions 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

Note

To search host reservations by hostname, it is critical that the collation of the hostname column in the host table be case-insensitive. Fortunately, that is the default in MySQL, but it can be verified via this command:

mysql> SELECT COLLATION('');
+-----------------+
| COLLATION('')   |
+-----------------+
| utf8_general_ci |
+-----------------+

According to mysql's naming convention, when the name ends in _ci, the collation is case-insensitive.

4.3.2.4. Improved Performance With MySQL

Changing the MySQL internal value innodb_flush_log_at_trx_commit from the default value of 1 to 2 can result in a huge gain in Kea performance. In some deployments, the gain was over 1000% (10 times faster when set to 2, compared to the default value of 1). It can be set per-session for testing:

mysql> SET GLOBAL innodb_flush_log_at_trx_commit=2;
mysql> SHOW SESSION VARIABLES LIKE 'innodb_flush_log%';

or permanently in /etc/mysql/my.cnf:

[mysqld]
innodb_flush_log_at_trx_commit=2

Be aware that changing this value can cause problems during data recovery after a crash, so we recommend checking the MySQL documentation. With the default value of 1, MySQL writes changes to disk after every INSERT or UPDATE query (in Kea terms, every time a client gets a new lease or renews an existing lease). When innodb_flush_log_at_trx_commit is set to 2, MySQL writes the changes at intervals no longer than 1 second. Batching writes gives a substantial performance boost. The trade-off, however, is that in the worst-case scenario, all changes in the last second before crash could be lost. Given the fact that Kea is stable software and crashes very rarely, most deployments find it a beneficial trade-off.

4.3.3. PostgreSQL

PostgreSQL can store leases, host reservations, and options defined on a per-host basis.

4.3.3.1. First-Time Creation of the PostgreSQL Database

Before preparing any Kea-specific database and tables, the PostgreSQL database must be configured to use the system timezone. It is recommended to use UTC as the timezone for both the system and the PostgreSQL database.

To check the system timezone:

date +%Z

To check the PostgreSQL timezone:

postgres=# show timezone;
postgres=# SELECT * FROM pg_timezone_names WHERE name = current_setting('TIMEZONE');

To configure the PostgreSQL timezone for a specific server, please refer to the installed version documentation.

Usually the setting is configured in the postgresql.conf with the varying version path /etc/postgresql/<version>/main/postgresql.conf, but on some systems the files may be located in /var/lib/pgsql/data.

timezone = 'UTC'

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 "postgres":

   $ 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=# \c database-name
   You are now connected to database "database-name" as user "postgres".
   postgres=# GRANT ALL PRIVILEGES ON SCHEMA public 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. 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 is /etc/postgresql/*/main/postgresql.conf. However, on some systems, the file may reside in /var/lib/pgsql/data.

   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 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 accidentally irretrievable mistakes by kea-admin.)

4.3.3.3. Upgrading a PostgreSQL Engine From an Earlier Version

If you upgraded your PostgreSQL from a version prior to 15.0, you need to grant additional privileges to the user:

First, log into PostgreSQL as "postgres":

$ sudo -u postgres psql -d database-name -U postgres
Enter password:
postgres=#

Next, grant the access to the public schema.

postgres=# GRANT ALL PRIVILEGES ON SCHEMA public TO user-name;
GRANT
postgres=#

Now, quit the PostgreSQL client:

postgres=# \q
Bye
$

4.3.3.4. 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

4.3.3.5. PostgreSQL without OpenSSL support

Usually the PostgreSQL database client library is built with the OpenSSL support but Kea can be configured to handle the case where it is not supported:

$ ./configure [other-options] --disable-pgsql-ssl

4.3.3.6. Improved Performance With PostgreSQL

Changing the PostgreSQL internal value synchronous_commit from the default value of ON to OFF can result in significant gains in Kea performance; on slow systems, the gain can be over 1000%. It can be set per-session for testing:

postgres=# SET synchronous_commit = OFF;

or permanently via command (preferred method):

postgres=# ALTER SYSTEM SET synchronous_commit=OFF;

or permanently in /etc/postgresql/[version]/main/postgresql.conf:

synchronous_commit = off

Changing this value can cause problems during data recovery after a crash, so we recommend a careful read of the PostgreSQL documentation. With the default value of ON, PostgreSQL writes changes to disk after every INSERT or UPDATE query (in Kea terms, every time a client gets a new lease or renews an existing lease). When synchronous_commit is set to OFF, PostgreSQL adds some delay before writing the changes. Batching writes gives a substantial performance boost, but in the worst-case scenario, all changes in the last moment before a crash could be lost. Since Kea is stable software and crashes very rarely, most deployments find the performance benefits outweigh the potential risks.

4.3.4. 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.

4.3.5. Limitations Related to the Use of SQL Databases

4.3.5.1. Year 2038 Issue

The lease expiration time in Kea is stored in the SQL database for each lease as a timestamp value. Kea developers have observed that the MySQL database does not accept timestamps beyond 2147483647 seconds (the maximum signed 32-bit number) from the beginning of the UNIX epoch (00:00:00 on 1 January 1970). Some versions of PostgreSQL do accept greater values, but the value is altered when it is read back. For this reason, the lease database backends put a restriction on the maximum timestamp to be stored in the database, which is equal to the maximum signed 32-bit number. This effectively means that the current Kea version cannot store leases whose expiration time is later than 2147483647 seconds since the beginning of the epoch (around the year 2038). This will be fixed when database support for longer timestamps is available.