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6.2.5 Ensure ‘Log_hostname’ Database Flag for Cloud SQL PostgreSQL Instance Is Set to 'on' (Automated)​

Profile Applicability​

• Level 1

Description​

PostgreSQL logs only the IP address of the connecting hosts. The log_hostname flag controls the logging of hostnames in addition to the IP addresses logged. The performance hit is dependent on the configuration of the environment and the host name resolution setup. This parameter can only be set in the postgresql.conf file or on the server command line.

Rationale​

Logging hostnames allows for the association of hostname to IP address at the time of connection. This information can aid with incident response efforts particularly in an environment that utilized dynamic IP addresses. Logging hostnames may incur overhead on server performance as for each statement logged, DNS resolution will be required to convert IP address to hostname. Depending on the setup, this may be non-negligible. This recommendation is applicable to PostgreSQL database instances.

Impact​

Setting custom flags via command line on certain instances will cause all omitted flags to be reset to defaults. This may cause you to lose custom flags and could result in unforeseen complications or instance restarts. Because of this, it is recommended you apply these flags changes during a period of low usage.

Audit​

From Console:

  1. Go to the Cloud SQL Instances page in the Google Cloud Console by visiting https://console.cloud.google.com/sql/instances.
  2. Select the instance to open its Instance Overview page
  3. Go to Configuration card
  4. Under Database flags, check the value of log_hostname flag is set to 'On'.

From Command Line:

  1. Use the below command for every Cloud SQL PostgreSQL database instance to verify the value of log_hostname
gcloud sql instances list --format=json | jq '.settings.databaseFlags[] | select(.name=="log_hostname")|.value'

Remediation​

From Console:

  1. Go to the Cloud SQL Instances page in the Google Cloud Console by visiting https://console.cloud.google.com/sql/instances.
  2. Select the PostgreSQL instance for which you want to enable the database flag.
  3. Click Edit.
  4. Scroll down to the Flags section.
  5. To set a flag that has not been set on the instance before, click Add item, choose the flag log_hostname from the drop-down menu and the value to On.
  6. Click Save to save your changes.
  7. Confirm your changes under Flags on the Overview page.

From Command Line:

  1. Configure the log_hostname database flag for every Cloud SQL PosgreSQL database instance using the below command.
gcloud sql instances patch <INSTANCE_NAME> --database-flags log_hostname=on
note

This command will overwrite all database flags previously set. To keep those and add new ones, include the values for all flags you want set on the instance; any flag not specifically included is set to its default value. For flags that do not take a value, specify the flag name followed by an equals sign ("=").

References​

https://cloud.google.com/sql/docs/postgres/flags
https://www.postgresql.org/docs/current/runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHAT

Additional Information​

warning

This patch modifies database flag values, which may require your instance to be restarted. Check the list of supported flags - https://cloud.google.com/sql/docs/postgres/flags - to see if your instance will be restarted when this patch is submitted.

note

Some database flag settings can affect instance availability or stability and remove the instance from the Cloud SQL SLA. For information about these flags, see Operational Guidelines.

note

Configuring the above flag does not require restarting the Cloud SQL instance.