6.1. The pool_hba.conf File

Just like the pg_hba.conf file for PostgreSQL, Pgpool-II supports a similar client authentication function using a configuration file called pool_hba.conf. If Pgpool-II is installed from source code, it also includes the sample pool_hba.conf.sample file in the default configuration directory ("/usr/local/etc"). By default, pool_hba authentication is disabled, and setting enable_pool_hba to on enables it. see the enable_pool_hba configuration parameter.

Note: If number of PostgreSQL servers is only one, or when running in raw mode (see Section 3.3.2), pool_hba.conf is not necessary thus enable_pool_hba may be being set to off. In this case the client authentication method is completely managed by PostgreSQL. Also number of PostgreSQL servers is more than one, or not running in raw mode, enable_pool_hba may be being set to off as long as the authentication method defined by PostgreSQL is trust.

The format of the pool_hba.conf file follows very closely PostgreSQL's pg_hba.conf format.

The general format of the pool_hba.conf file is a set of records, one per line. Blank lines are ignored, as is any text after the # comment character. Records cannot be continued across lines. A record is made up of a number of fields which are separated by spaces and/or tabs. Fields can contain white space if the field value is double-quoted. Quoting one of the keywords in a database, user, or address field (e.g., all or replication) makes the word lose its special meaning, and just match a database, user, or host with that name.

Each record specifies a connection type, a client IP address range (if relevant for the connection type), a database name, a user name, and the authentication method to be used for connections matching these parameters. The first record with a matching connection type, client address, requested database, and user name is used to perform authentication. There is no "fall-through" or "backup": if one record is chosen and the authentication fails, subsequent records are not considered. If no record matches, access is denied.

A record can have one of the following formats

    local      database  user  auth-method  [auth-options]

    host       database  user  IP-address IP-mask  auth-method  [auth-options]
    hostssl    database  user  IP-address IP-mask  auth-method  [auth-options]
    hostnossl  database  user  IP-address IP-mask  auth-method  [auth-options]

    host       database  user  address  auth-method  [auth-options]
    hostssl    database  user  address  auth-method  [auth-options]
    hostnossl  database  user  address  auth-method  [auth-options]

The meaning of the fields is as follows:


This record matches connection attempts using Unix-domain sockets. Without a record of this type, Unix-domain socket connections are disallowed.


This record matches connection attempts made using TCP/IP. host records match either SSL or non-SSL connection attempts.

Note: Remote TCP/IP connections will not be possible unless the server is started with an appropriate value for the listen_addresses configuration parameter, since the default behavior is to listen for TCP/IP connections only on the local loopback address localhost.


This record matches connection attempts made using TCP/IP, but only when the connection is made with SSL encryption.

To make use of this option the Pgpool-II must be built with SSL support. Furthermore, SSL must be enabled by setting the ssl configuration parameter. Otherwise, the hostssl record is ignored.


This record type has the opposite behavior of hostssl; it only matches connection attempts made over TCP/IP that do not use SSL.


Specifies which database name(s) this record matches. The value all specifies that it matches all databases.

Note: "samegroup" for database field is not supported:

Since Pgpool-II does not know anything about users in the PostgreSQL backend server, the database name is simply compared against the entries in the database field of pool_hba.conf.


Specifies which database user name(s) this record matches. The value all specifies that it matches all users. Otherwise, this is the name of a specific database user

Note: group names following "+" for user field is not supported:

This is for the same reason as for the "samegroup" of database field. A user name is simply checked against the entries in the user field of pool_hba.conf.


Specifies the client machine address(es) that this record matches. This field can contain either a host name, an IP address range, or one of the special key words mentioned below.

An IP address range is specified using standard numeric notation for the range's starting address, then a slash (/) and a CIDR mask length. The mask length indicates the number of high-order bits of the client IP address that must match. Bits to the right of this should be zero in the given IP address. There must not be any white space between the IP address, the /, and the CIDR mask length.

Typical examples of an IPv4 address range specified this way are for a single host, or for a small network, or for a larger one. An IPv6 address range might look like ::1/128 for a single host (in this case the IPv6 loopback address) or fe80::7a31:c1ff:0000:0000/96 for a small network. represents all IPv4 addresses, and ::0/0 represents all IPv6 addresses. To specify a single host, use a mask length of 32 for IPv4 or 128 for IPv6. In a network address, do not omit trailing zeroes.

An entry given in IPv4 format will match only IPv4 connections, and an entry given in IPv6 format will match only IPv6 connections, even if the represented address is in the IPv4-in-IPv6 range. Note that entries in IPv6 format will be rejected if the system's C library does not have support for IPv6 addresses.

You can also write all to match any IP address, samehost to match any of the server's own IP addresses, or samenet to match any address in any subnet that the server is directly connected to.

If a host name is specified (anything that is not an IP address range or a special key word is treated as a host name), that name is compared with the result of a reverse name resolution of the client's IP address (e.g., reverse DNS lookup, if DNS is used). Host name comparisons are case insensitive. If there is a match, then a forward name resolution (e.g., forward DNS lookup) is performed on the host name to check whether any of the addresses it resolves to are equal to the client's IP address. If both directions match, then the entry is considered to match. (The host name that is used in pool_hba.conf should be the one that address-to-name resolution of the client's IP address returns, otherwise the line won't be matched. Some host name databases allow associating an IP address with multiple host names, but the operating system will only return one host name when asked to resolve an IP address.)

A host name specification that starts with a dot (.) matches a suffix of the actual host name. So .example.com would match foo.example.com (but not just example.com).

When host names are specified in pool_hba.conf, you should make sure that name resolution is reasonably fast. It can be of advantage to set up a local name resolution cache such as nscd.

This field only applies to host, hostssl, and hostnossl records.

Specifying the host name in address field is not supported prior to Pgpool-II V3.7.


These two fields can be used as an alternative to the IP-address/ mask-length notation. Instead of specifying the mask length, the actual mask is specified in a separate column. For example, represents an IPv4 CIDR mask length of 8, and represents a CIDR mask length of 32.

This field only applies to host, hostssl, and hostnossl records.


Specifies the authentication method to use when a connection matches this record. The possible choices are summarized here; details are in Section 6.2.


Allow the connection unconditionally. This method allows anyone that can connect to the Pgpool-II.


Reject the connection unconditionally. This is useful for "filtering out" certain hosts, for example a reject line could block a specific host from connecting.


Require the client to supply a double-MD5-hashed password for authentication.

Note: To use md5 authentication, you need to register the user name and password in pool_passwd file. See Section 6.2.3 for more details. If you don't want to manage password by using pool_passwd, you could use allow_clear_text_frontend_auth.


Perform SCRAM-SHA-256 authentication to verify the user's password.

Note: To use scram-sha-256 authentication, you need to register the user name and password in pool_passwd file. See Section 6.2.4 for more details. If you don't want to manage password by using pool_passwd, you could use allow_clear_text_frontend_auth.


Authenticate using SSL client certificates. See Section 6.2.5 for more details.


Authenticate using the Pluggable Authentication Modules (PAM) service provided by the operating system. See Section 6.2.6 for details.

PAM authentication is supported using user information on the host where Pgpool-II is running. To enable PAM support the Pgpool-II must be configured with "--with-pam"

To enable PAM authentication, you must create a service-configuration file for Pgpool-II in the system's PAM configuration directory (that is usually located at "/etc/pam.d"). A sample service-configuration file is also installed as "share/pgpool.pam" under the install directory.


Authenticate using LDAP server. See Section 6.2.7 for more details.

To enable LDAP support the Pgpool-II must be configured with "--with-ldap"


After the auth-method field, there can be field(s) of the form name= value that specify options for the authentication method.

Since the pool_hba.conf records are examined sequentially for each connection attempt, the order of the records is significant. Typically, earlier records will have tight connection match parameters and weaker authentication methods, while later records will have looser match parameters and stronger authentication methods. For example, one might wish to use trust authentication for local TCP/IP connections but require a password for remote TCP/IP connections. In this case a record specifying trust authentication for connections from would appear before a record specifying password authentication for a wider range of allowed client IP addresses.

Tip: All pool_hba authentication options described in this section are about the authentication taking place between a client and the Pgpool-II. A client still has to go through the PostgreSQL's authentication process and must have the CONNECT privilege for the database on the backend PostgreSQL server.

As far as pool_hba is concerned, it does not matter if a user name and/or database name given by a client (i.e. psql -U testuser testdb) really exists in the backend. pool_hba only cares if a match in the pool_hba.conf can be found or not.

Some examples of pool_hba.conf entries. See the next section for details on the different authentication methods.

Example 6-1. Example pool_hba.conf Entries

    # Allow any user on the local system to connect to any database with
    # any database user name using Unix-domain sockets (the default for local
    # connections).
    # TYPE  DATABASE        USER            ADDRESS                 METHOD
    local   all             all                                     trust

    # The same using local loopback TCP/IP connections.
    # TYPE  DATABASE        USER            ADDRESS                 METHOD
    host    all             all               trust

    # Allow any user from host to connect to database
    # "postgres" if the user's password is correctly supplied.
    # TYPE  DATABASE        USER            ADDRESS                 METHOD
    host    postgres        all           md5