Configuring HARP

TPA installs and configures HARP when failover_manager is set to harp . This value is the default for BDR-Always-ON clusters.

Installing HARP

You must provide the harp-manager and harp-proxy packages. Contact EDB to obtain access to these packages.

Configuring HARP

See the HARP documentation

for more details on HARP configuration.

Variable	Default value	Description
cluster_name	``	The name of the cluster.
harp_consensus_protocol	` `	The consensus layer to use (etcd or bdr).
harp_location	location	The location of this instance (defaults to the location parameter).
harp_ready_status_duration	10	Amount of time in seconds the node's readiness status persists if not refreshed.
harp_leader_lease_duration	6	Amount of time in seconds the Lead Master lease persists if not refreshed.
harp_lease_refresh_interval	2000	Amount of time in milliseconds between refreshes of the Lead Master lease.
harp_dcs_reconnect_interval	1000	The interval, measured in ms, between attempts that a disconnected node tries to reconnect to the DCS.
harp_dcs_priority	500	In the case in which two nodes have an equal amount of lag and other qualified criteria to take the Lead Master lease, acts as an additional ranking value to prioritize one node over another.
harp_stop_database_when_fenced	false	Rather than removing a node from all possible routing, stop the database on a node when it's fenced.
harp_fenced_node_on_dcs_failure	false	If HARP is unable to reach the DCS, then fence the node.
harp_maximum_lag	1048576	Highest allowable variance (in bytes) between last recorded LSN of previous Lead Master and this node before being allowed to take the Lead Master lock.
harp_maximum_camo_lag	1048576	Highest allowable variance (in bytes) between last received LSN and applied LSN between this node and its CAMO partners.
harp_camo_enforcement	lag_only	Whether to strictly enforce CAMO queue state.
harp_use_unix_sock	false	Use Unix domain socket for manager database access.
harp_request_timeout	250	Time in milliseconds to allow a query to the DCS to succeed.
harp_watch_poll_interval	500	Milliseconds to sleep between polling DCS. Applies only when harp_consensus_protocol is bdr.
harp_proxy_timeout	1	Builtin proxy connection timeout, in seconds, to Lead Master.
harp_proxy_keepalive	5	Amount of time builtin proxy waits on an idle connection to the Lead Master before sending a keepalive ping.
harp_proxy_max_client_conn	75	Maximum number of client connections accepted by harp-proxy (max_client_conn).
harp_ssl_password_command	None	A custom command to receive the obfuscated sslpassword in the stdin and provide the handled sslpassword via stdout.
harp_db_request_timeout	10s	Similar to dcs -> request_timeout but for connection to the database.

You can use the harp-config hook

to execute tasks after the HARP configuration files are installed, for example, to install additional configuration files.

Consensus layer

The --harp-consensus-protocol argument to tpaexec configure is mandatory for the BDR-Always-ON architecture.

etcd

If the --harp-consensus-protocol etcd option is given to tpaexec configure , then TPA sets harp_consensus_protocol to etcd in config.yml . It gives the etcd role to a suitable subset of the instances, depending on your chosen layout.

HARP v2 requires etcd v3.5.0 or later, which is available in the products/harp/release package repositories provided by EDB.

You can configure the following parameters for etcd,

Variable	Default value	Description
etcd_peer_port	2380	The port used by etcd for peer communication
etcd_client_port	2379	The port used by clients to connect to etcd

bdr

If the --harp-consensus-protocol bdr option is given to tpaexec configure , then TPA sets harp_consensus_protocol to bdr in config.yml . In this case, the existing PGD instances are used for consensus, and no further configuration is required.

Configuring a separate user for HARP proxy

If you want HARP proxy to use a separate read-only user, you can specify that by setting harp_dcs_user: username under cluster_vars . TPA uses the harp_dcs_user setting to create a read-only user and set it up in the DCS configuration.

Configuring a separate user for HARP manager

If you want HARP manager to use a separate user, you can specify that by setting harp_manager_user: username under cluster_vars . TPA uses that setting to create a new user and grant it the bdr_superuser role.

Custom SSL password command

The command provided by harp_ssl_password_command is used by HARP to de-obfuscate the sslpassword given in the connection string. If sslpassword isn’t present, then harp_ssl_password_command is ignored. If sslpassword isn’t obfuscated, then harp_ssl_password_command isn’t required and should not be specified.

Configuring the HARP service

You can configure the following parameters for the HARP service.

Variable	Default value	Description
harp_manager_restart_on_failure	false	If true, the harp-manager service is overridden so it's restarted on failure. The default is false to comply with the service installed by the harp-manager package.

Configuring HARP http(s) health probes

You can enable and configure the http(s) service for HARP that provides API endpoints to monitor the service’s health.

Variable	Default value	Description
harp_http_options	enable: false``secure: false``host: <inventory_hostname>``port: 8080``probes:  timeout: 10s``endpoint: "host=<proxy_name> port=<6432> dbname=<bdrdb> user=<username>"	Configure the http section of HARP config.yml that defines the http(s) API settings.

The variable can contain these keys:

enable: false
secure: false
cert_file: "/etc/tpa/harp_proxy/harp_proxy.crt"
key_file: "/etc/tpa/harp_proxy/harp_proxy.key"
host: <inventory_hostname>
port: 8080
probes:
  timeout: 10s
endpoint: "<valid dsn>"

The cert_file and key_file keys are both required if you use secure: true and are willing to use your own certificate and key.

You must ensure that both certificate and key are available at the given location on the target node before running deploy .

Leave both cert_file and key_file empty if you want TPA to generate a certificate and key for you using a cluster-specific CA certificate. TPA CA certificate isn’t “well-known.” You need to add this certificate to the trust store of each machine that probes the endpoints. The CA certificate can be found on the cluster directory on the TPA node at <cluster_dir>/ssl/CA.crt after deploy .

See the HARP documentation for more information about the available API endpoints.