Using SSL with a PostgreSQL DB instance

Amazon RDS supports Secure Socket Layer (SSL) encryption for PostgreSQL DB instances. Using SSL, you can encrypt a PostgreSQL connection between your applications and your PostgreSQL DB instances. By default, RDS for PostgreSQL uses and expects all clients to connect using SSL/TLS, but you can also require it. RDS for PostgreSQL supports Transport Layer Security (TLS) versions 1.1, 1.2, and 1.3.

For general information about SSL support and PostgreSQL databases, see SSL support in the PostgreSQL documentation. For information about using an SSL connection over JDBC, see Configuring the client in the PostgreSQL documentation.

SSL support is available in all AWS Regions for PostgreSQL. Amazon RDS creates an SSL certificate for your PostgreSQL DB instance when the instance is created. If you enable SSL certificate verification, then the SSL certificate includes the DB instance endpoint as the Common Name (CN) for the SSL certificate to guard against spoofing attacks.

Connecting to a PostgreSQL DB instance over SSL

To connect to a PostgreSQL DB instance over SSL

1. Download the certificate.

   For information about downloading certificates, see Using SSL/TLS to encrypt a connection to a DB instance or cluster.

2. Connect to your PostgreSQL DB instance over SSL.

   When you connect using SSL, your client can choose whether to verify the certificate chain. If your connection parameters specify sslmode=verify-ca or sslmode=verify-full, then your client requires the RDS CA certificates to be in their trust store or referenced in the connection URL. This requirement is to verify the certificate chain that signs your database certificate.

   When a client, such as psql or JDBC, is configured with SSL support, the client first tries to connect to the database with SSL by default. If the client can't connect with SSL, it reverts to connecting without SSL. The default sslmode mode used is different between libpq-based clients (such as psql) and JDBC. The libpq-based clients default to prefer, and JDBC clients default to verify-full.

   Use the sslrootcert parameter to reference the certificate, for example sslrootcert=rds-ssl-ca-cert.pem.

The following is an example of using psql to connect to a PostgreSQL DB instance using SSL with certificate verification.

$ psql "host=db-name.555555555555.ap-southeast-1.rds.amazonaws.com 
    port=5432 dbname=testDB user=testuser sslrootcert=rds-ca-rsa2048-g1.pem sslmode=verify-full"

Requiring an SSL connection to a PostgreSQL DB instance

You can require that connections to your PostgreSQL DB instance use SSL by using the rds.force_ssl parameter. The rds.force_ssl parameter default value is 1 (on) for RDS for PostgreSQL version 15 and later. For all other RDS for PostgreSQL major versions 14 and older, the default value of this parameter is 0 (off). You can set the rds.force_ssl parameter to 1 (on) to require SSL/TLS for connections to your DB cluster. You can set the rds.force_ssl parameter to 1 (on) to require SSL for connections to your DB instance.

To change the value of this parameter, you need to create a custom DB parameter group. You then change the value for rds.force_ssl in your custom DB parameter group to 1 to turn on this feature. If you prepare the custom DB parameter group before creating your RDS for PostgreSQL DB instance you can choose it (instead of a default parameter group) during the creation process. If you do this after your RDS for PostgreSQL DB instance is already running, you need to reboot the instance so that your instance uses the custom parameter group. For more information, see Parameter groups for Amazon RDS.

When the rds.force_ssl feature is active on your DB instance, connection attempts that aren't using SSL are rejected with the following message:

$ psql -h db-name.555555555555.ap-southeast-1.rds.amazonaws.com port=5432 dbname=testDB user=testuser
psql: error: FATAL: no pg_hba.conf entry for host "w.x.y.z", user "testuser", database "testDB", SSL off

Determining the SSL connection status

The encrypted status of your connection is shown in the logon banner when you connect to the DB instance:

Password for user master: 
psql (10.3) 
SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256) 
Type "help" for help.
postgres=> 

You can also load the sslinfo extension and then call the ssl_is_used() function to determine if SSL is being used. The function returns t if the connection is using SSL, otherwise it returns f.

postgres=> CREATE EXTENSION sslinfo;
CREATE EXTENSION
postgres=> SELECT ssl_is_used();
ssl_is_used
---------
t
(1 row)

For more detailed information, you can use the following query to get information from pg_settings:

SELECT name as "Parameter name", setting as value, short_desc FROM pg_settings WHERE name LIKE '%ssl%';
             Parameter name             |                  value                  |                      short_desc
----------------------------------------+-----------------------------------------+-------------------------------------------------------
 ssl                                    | on                                      | Enables SSL connections.
 ssl_ca_file                            | /rdsdbdata/rds-metadata/ca-cert.pem     | Location of the SSL certificate authority file.
 ssl_cert_file                          | /rdsdbdata/rds-metadata/server-cert.pem | Location of the SSL server certificate file.
 ssl_ciphers                            | HIGH:!aNULL:!3DES                       | Sets the list of allowed SSL ciphers.
 ssl_crl_file                           |                                         | Location of the SSL certificate revocation list file.
 ssl_dh_params_file                     |                                         | Location of the SSL DH parameters file.
 ssl_ecdh_curve                         | prime256v1                              | Sets the curve to use for ECDH.
 ssl_key_file                           | /rdsdbdata/rds-metadata/server-key.pem  | Location of the SSL server private key file.
 ssl_library                            | OpenSSL                                 | Name of the SSL library.
 ssl_max_protocol_version               |                                         | Sets the maximum SSL/TLS protocol version to use.
 ssl_min_protocol_version               | TLSv1.2                                 | Sets the minimum SSL/TLS protocol version to use.
 ssl_passphrase_command                 |                                         | Command to obtain passphrases for SSL.
 ssl_passphrase_command_supports_reload | off                                     | Also use ssl_passphrase_command during server reload.
 ssl_prefer_server_ciphers              | on                                      | Give priority to server ciphersuite order.
(14 rows)

You can also collect all the information about your RDS for PostgreSQL DB instance's SSL usage by process, client, and application by using the following query:

SELECT datname as "Database name", usename as "User name", ssl, client_addr, application_name, backend_type
   FROM pg_stat_ssl
   JOIN pg_stat_activity
   ON pg_stat_ssl.pid = pg_stat_activity.pid
   ORDER BY ssl;
 Database name | User name | ssl |  client_addr   |    application_name    |         backend_type
---------------+-----------+-----+----------------+------------------------+------------------------------
               |           | f   |                |                        | autovacuum launcher
               | rdsadmin  | f   |                |                        | logical replication launcher
               |           | f   |                |                        | background writer
               |           | f   |                |                        | checkpointer
               |           | f   |                |                        | walwriter
 rdsadmin      | rdsadmin  | t   | 127.0.0.1      |                        | client backend
 rdsadmin      | rdsadmin  | t   | 127.0.0.1      | PostgreSQL JDBC Driver | client backend
 postgres      | postgres  | t   | 204.246.162.36 | psql                   | client backend
(8 rows)

To identify the cipher used for your SSL connection, you can query as follows:

postgres=> SELECT ssl_cipher();
ssl_cipher
--------------------
DHE-RSA-AES256-SHA
(1 row)

To learn more about the sslmode option, see Database connection control functions in the PostgreSQL documentation.

SSL cipher suites in RDS for PostgreSQL

The PostgreSQL configuration parameter ssl_ciphers specifies the categories of cipher suites that are allowed for SSL connections. The following table lists the default cipher suites used in RDS for PostgreSQL.

PostgreSQL engine version	Cipher suites
16	HIGH:!aNULL:!3DES
15	HIGH:!aNULL:!3DES
14	HIGH:!aNULL:!3DES
13	HIGH:!aNULL:!3DES
12	HIGH:!aNULL:!3DES
11.4 and higher minor versions	HIGH:MEDIUM:+3DES:!aNULL:!RC4
11.1, 11.2	HIGH:MEDIUM:+3DES:!aNULL
10.9 and higher minor versions	HIGH:MEDIUM:+3DES:!aNULL:!RC4
10.7 and lower minor versions	HIGH:MEDIUM:+3DES:!aNULL