HARP Proxy

HARP Proxy is a daemon that acts as an abstraction layer between the client application and Postgres. It interfaces with the consensus layer to obtain the identity of the current lead master node and directs traffic to that location. During a planned switchover or unplanned failover, it redirects to the new lead master node as dictated by the DCS.

You can select between pgbouncer or builtin for HARP Proxy. If you don’t specify a proxy type, the default is builtin . When using pgbouncer , HARP Proxy is an interface layer between the DCS and PgBouncer. As such, PgBouncer is a prerequisite and must also be installed for HARP Proxy to fully manage its activity.

The builtin proxy doesn’t require any additional software. When using builtin, HARP Proxy functions as a level 4 pass-through proxy.

Builtin proxy: how it works

Upon starting, HARP Proxy listens for incoming connections on the listening address and listening port specified in the bootstrap file per proxy instance. All application client traffic then passes through builtin proxy into the current lead master node for the location where this proxy is operating.

If the lead master lease isn’t set, HARP Proxy disconnects all connection traffic until a new lead master is established. This also applies to circumstances when harpctl promote is used to invoke a planned transition to a new lead master. The disconnect is immediate.

Configuration

Choose the built-in proxy by setting the proxy type to builtin . The only other option that applies to the built-in proxy is max_client_conn , which specifies the maximum allowed client connections. If max_client_conn is higher than what the system can handle, it is lowered to a setting that’s within the capability of the system that the proxy is on.

PgBouncer: how it works

Note

If you need more configurability of pgbouncer than what Harp Proxy provides, the recommended setup is to use builtin proxy and have pgbouncer point to it.

Upon starting, HARP Proxy launches PgBouncer if it’s not already running and leaves client connections paused. After, it contacts the DCS to determine the identity of the lead master, configure PgBouncer to use this as the target for database connections, and resume connection activity. All application client traffic then passes through PgBouncer into the current lead master node for the location where this proxy is operating.

While PgBouncer is running, HARP Proxy checks its status based on the monitor_interval configuration setting in the DCS and stores it in the DCS for monitoring purposes. This configuration allows interrogation with harpctl to retrieve status of all configured proxies or any one proxy.

If the lead master lease isn’t set, HARP Proxy pauses all connection traffic until a new lead master is established. This also applies to circumstances when harpctl promote is used to invoke a planned transition to a new lead master. It uses a PgBouncer PAUSE command for this, so existing sessions are allowed to complete any pending transactions before they’re held in stasis.

PgBouncer configuration file

When HARP Proxy uses PgBouncer for connection management and redirection, a pgbouncer.ini file must exist. HARP Manager builds this file based on various runtime directives as defined in

Proxy directives .

This file is located in the same folder as the config.yml used by HARP Proxy. Any PgBouncer process launched by HARP Proxy uses this configuration file, and you can use it for debugging or information purposes. Modifications to this automatically generated pgbouncer.ini file are lost any time HARP Proxy restarts, so use harpctl set proxy to alter these settings instead. Calling harpctl set proxy doesn’t update the pgbouncer.ini file until the proxy restarts.

Disabling and reenabling HARP Proxy node management

You can temporarily pause HARP Proxy control of PgBouncer. This results in a state where the daemon continues running but doesn’t perform any operations that can affect existing behavior of the cluster. Reenabling management causes it to resume operation.

An example of temporarily disabling management of a specific proxy is:

harpctl unmanage proxy proxy1

See harpctl command-line tool for more details.

Proxy node management is enabled by default.

Passthrough user authentication

With pgbouncer, we strongly recommend configuring HARP Proxy to use the auth_user and auth_query runtime directives. If these aren’t set, the PgBouncer userlist.txt file must include username and password hash combinations for every user PgBouncer needs to authenticate on behalf of Postgres.

Do not use the pgbouncer user, as this this is used by HARP Proxy as an admin-level user to operate the underlying PgBouncer service.

Configuration

HARP Proxy expects the dcs , cluster , and proxy configuration stanzas. The following is a functional example:

cluster:
  name: mycluster

dcs:
  driver: etcd
  endpoints:
    - host1:2379
    - host2:2379
    - host3:2379

proxy:
  name: proxy1
```  Each proxy connects to the DCS to retrieve the hosts and ports to listen on for connections.

###  Usage

This is the basic usage for HARP Proxy:

```bash
Usage of ./harp-proxy:
  -f string
        Optional path to config file (shorthand)
  --config string
        Optional path to config file

There are no arguments to launch harp-proxy as a forked daemon. This software is designed to be launched through systemd or in a container as a top-level process. This also means output is directed to STDOUT and STDERR for capture and access through journald or an attached container terminal.