Working with the supported foreign data wrappers for Amazon Aurora PostgreSQL
A foreign data wrapper (FDW) is a specific type of extension that provides access to external data. For example, the
oracle_fdw
extension allows your Aurora PostgreSQL DB instance
to work with Oracle databases.
Following, you can find information about several supported PostgreSQL foreign data wrappers.
Topics
Working with Oracle databases by using the oracle_fdw extension
To access an Oracle database from your Aurora PostgreSQL DB cluster
you can install and use the
oracle_fdw
extension. This extension is a foreign data wrapper for Oracle databases. To learn more about
this extension, see the oracle_fdw
The oracle_fdw
extension is supported on Aurora PostgreSQL 12.7 (Amazon Aurora release 4.2)
and higher versions.
Topics
Turning on the oracle_fdw extension
To use the oracle_fdw extension, perform the following procedure.
To turn on the oracle_fdw extension
-
Run the following command using an account that has
rds_superuser
permissions.CREATE EXTENSION oracle_fdw;
Example: Using a foreign server linked to an Amazon RDS for Oracle database
The following example shows the use of a foreign server linked to an Amazon RDS for Oracle database.
To create a foreign server linked to an RDS for Oracle database
-
Note the following on the RDS for Oracle DB instance:
-
Endpoint
-
Port
-
Database name
-
-
Create a foreign server.
test=>
CREATE SERVER oradb FOREIGN DATA WRAPPER oracle_fdw OPTIONS (dbserver '//
endpoint
:port
/DB_name
');CREATE SERVER
-
Grant usage to a user who doesn't have
rds_superuser
privileges, for exampleuser1
.test=>
GRANT USAGE ON FOREIGN SERVER oradb TO user1;
GRANT
-
Connect as
user1
, and create a mapping to an Oracle user.test=>
CREATE USER MAPPING FOR user1 SERVER oradb OPTIONS (user '
oracleuser'
, password 'mypassword'
);CREATE USER MAPPING
-
Create a foreign table linked to an Oracle table.
test=>
CREATE FOREIGN TABLE
mytab
(a int) SERVER oradb OPTIONS (table 'MYTABLE'
);CREATE FOREIGN TABLE
-
Query the foreign table.
test=>
SELECT * FROM mytab;
a --- 1 (1 row)
If the query reports the following error, check your security group and access control list (ACL) to make sure that both instances can communicate.
ERROR: connection for foreign table "mytab" cannot be established
DETAIL: ORA-12170: TNS:Connect timeout occurred
Working with encryption in transit
PostgreSQL-to-Oracle encryption in transit is based on a combination of client and server configuration parameters. For an
example using Oracle 21c, see About the Values for Negotiating Encryption and IntegrityACCEPTED
, meaning that the encryption depends on the Oracle database
server configuration.
If your database is on RDS for Oracle, see Oracle native network encryption to configure the encryption.
Understanding the pg_user_mappings view and permissions
The PostgreSQL catalog pg_user_mapping
stores the mapping from an
Aurora PostgreSQL user to the user on a foreign
data (remote) server. Access to the catalog is restricted, but you use the pg_user_mappings
view
to see the mappings. In the following, you can find an example that shows how permissions apply with an example
Oracle database, but this information applies more generally to any foreign data wrapper.
In the following output, you can find roles and permissions mapped to three different
example users. Users rdssu1
and rdssu2
are members of the
rds_superuser
role, and user1
isn't. The example uses the
psql
metacommand \du
to list existing roles.
test=>
\du
List of roles Role name | Attributes | Member of -----------------+------------------------------------------------------------+------------------------------------------------------------- rdssu1 | | {rds_superuser} rdssu2 | | {rds_superuser} user1 | | {}
All users, including users that have rds_superuser
privileges, are allowed to view
their own user mappings (umoptions
) in
the pg_user_mappings
table. As shown in the following example, when
rdssu1
tries to obtain all user mappings, an error is raised even though
rdssu1
rds_superuser
privileges:
test=>
SELECT * FROM pg_user_mapping;
ERROR: permission denied for table pg_user_mapping
Following are some examples.
test=>
SET SESSION AUTHORIZATION rdssu1;
SET
test=>
SELECT * FROM pg_user_mappings;
umid | srvid | srvname | umuser | usename | umoptions -------+-------+---------+--------+------------+---------------------------------- 16414 | 16411 | oradb | 16412 | user1 | 16423 | 16411 | oradb | 16421 | rdssu1 | {user=oracleuser,password=mypwd} 16424 | 16411 | oradb | 16422 | rdssu2 | (3 rows)
test=>
SET SESSION AUTHORIZATION rdssu2;
SET
test=>
SELECT * FROM pg_user_mappings;
umid | srvid | srvname | umuser | usename | umoptions -------+-------+---------+--------+------------+---------------------------------- 16414 | 16411 | oradb | 16412 | user1 | 16423 | 16411 | oradb | 16421 | rdssu1 | 16424 | 16411 | oradb | 16422 | rdssu2 | {user=oracleuser,password=mypwd} (3 rows)
test=>
SET SESSION AUTHORIZATION user1;
SET
test=>
SELECT * FROM pg_user_mappings;
umid | srvid | srvname | umuser | usename | umoptions -------+-------+---------+--------+------------+-------------------------------- 16414 | 16411 | oradb | 16412 | user1 | {user=oracleuser,password=mypwd} 16423 | 16411 | oradb | 16421 | rdssu1 | 16424 | 16411 | oradb | 16422 | rdssu2 | (3 rows)
Because of implementation differences between information_schema._pg_user_mappings
and
pg_catalog.pg_user_mappings
, a manually created rds_superuser
requires additional permissions
to view passwords in pg_catalog.pg_user_mappings
.
No additional permissions are required for an rds_superuser
to view passwords in
information_schema._pg_user_mappings
.
Users who don't have the rds_superuser
role can view passwords in pg_user_mappings
only
under the following conditions:
-
The current user is the user being mapped and owns the server or holds the
USAGE
privilege on it. -
The current user is the server owner and the mapping is for
PUBLIC
.
Working with SQL Server databases by using the tds_fdw extension
You can use the PostgreSQL tds_fdw
extension to access databases that support
the tabular data stream (TDS) protocol, such as Sybase and Microsoft SQL Server databases. This
foreign data wrapper lets you connect from your
Aurora PostgreSQL DB cluster to databases that
use the TDS protocol, including Amazon RDS for Microsoft SQL Server. For more information, see
tds-fdw/tds_fdw
The tds_fdw
extension is supported on Amazon Aurora PostgreSQL version 13.6 and
higher releases.
Setting up your RDS for PostgreSQL DB to use the tds_fdw extension
In the following procedures, you can find an example of setting up and using the tds_fdw
with an Aurora PostgreSQL DB cluster.
Before you can connect to a SQL Server database using tds_fdw
,
you need to get the following details for the instance:
Hostname or endpoint. For an RDS for SQL Server DB instance, you can find the endpoint by using the Console. Choose the Connectivity & security tab and look in the "Endpoint and port" section.
Port number. The default port number for Microsoft SQL Server is 1433.
Name of the database. The DB identifier.
You also need to provide access on the security group or the access control list (ACL) for the SQL Server port, 1433. Both the Aurora PostgreSQL DB cluster and the RDS for SQL Server DB instance need access to port 1433. If access isn't configured correctly, when you try to query the Microsoft SQL Server you see the following error message:
ERROR: DB-Library error: DB #: 20009, DB Msg: Unable to connect:
Adaptive Server is unavailable or does not exist (mssql2019
.aws-region
.rds.amazonaws.com), OS #: 0, OS Msg: Success, Level: 9
To use tds_fdw to connect to a SQL Server database
Connect to your Aurora PostgreSQL DB cluster's primary instance using an account that has the
rds_superuser
role:psql --host=
your-cluster-name-instance-1
.aws-region
.rds.amazonaws.com --port=5432 --username=test –-passwordInstall the
tds_fdw
extension:test=>
CREATE EXTENSION tds_fdw;
CREATE EXTENSION
After the extension is installed on your Aurora PostgreSQL DB cluster , you set up the foreign server.
To create the foreign server
Perform these tasks on the Aurora PostgreSQL DB cluster
using an account that has
rds_superuser
privileges.
Create a foreign server in the Aurora PostgreSQL DB cluster:
test=>
CREATE SERVER
sqlserverdb
FOREIGN DATA WRAPPER tds_fdw OPTIONS (servername 'mssql2019
.aws-region
.rds.amazonaws.com', port '1433', database 'tds_fdw_testing
');CREATE SERVER
Grant permissions to a user who doesn't have
rds_superuser
role privileges, for example,user1
:test=>
GRANT USAGE ON FOREIGN SERVER
sqlserverdb
TOuser1
;Connect as user1 and create a mapping to a SQL Server user:
test=>
CREATE USER MAPPING FOR user1 SERVER
sqlserverdb
OPTIONS (username 'sqlserveruser
', password 'password
');CREATE USER MAPPING
Create a foreign table linked to a SQL Server table:
test=>
CREATE FOREIGN TABLE mytab (a int) SERVER
sqlserverdb
OPTIONS (table 'MYTABLE
');CREATE FOREIGN TABLE
Query the foreign table:
test=>
SELECT * FROM mytab;
a --- 1 (1 row)
Using encryption in transit for the connection
The connection from Aurora PostgreSQL to SQL Server uses encryption in transit (TLS/SSL) depending on the SQL Server database configuration. If the SQL Server isn't configured for encryption, the RDS for PostgreSQL client making the request to the SQL Server database falls back to unencrypted.
You can enforce encryption for the connection to RDS for SQL Server DB instances by
setting the rds.force_ssl
parameter. To learn how,
see Forcing
connections to your DB instance to use SSL. For more information about SSL/TLS
configuration for RDS for SQL Server, see Using
SSL with a Microsoft SQL Server DB instance.