How to Build a Dynamic PowerDNS Pipe Backend in Python

The PowerDNS Pipe Backend allows developers to attach custom external scripts (written in Python, Perl, Bash, or Go) to resolve DNS queries dynamically over standard I/O streams. This approach is ideal for dynamically serving CNAME aliases, geo-routing records, or integrating DNS responses with external APIs without rebuilding PowerDNS.

Environment: PowerDNS 3.x / 4.x • pdns-backend-pipe • Python IPC

1. Installing PowerDNS Pipe Backend (CentOS / RHEL)

yum install pdns pdns-backend-pipe -y

Configure /etc/pdns/pdns.conf to launch the pipe backend alongside standard zone providers:

launch=bind,pipe
pipe-command=/etc/pdns/pdns-backend.py

2. The Python Backend Script (/etc/pdns/pdns-backend.py)

The script communicates with PowerDNS via tab-delimited protocol over stdin/stdout. Note the -u flag on Python to ensure unbuffered I/O:

#!/usr/bin/python -u
from sys import stdin, stdout

# Handshake initialization
data = stdin.readline()
stdout.write("OK	My Dynamic Python Backend
")
stdout.flush()

TARGET_CNAME = 'cname-target.example.com'

while True:
    line = stdin.readline()
    if not line:
        break
    data = line.strip()
    kind, qname, qclass, qtype, qid, ip = data.split('	')
    
    if kind == 'Q' and qname not in TARGET_CNAME:
        # Provide SOA record for authoritative delegation
        soa_resp = f"DATA	{qname}	{qclass}	SOA	86400	-1	support.{qname} ns1.example.org 2026010100 1800 3600 604800 3600
"
        stdout.write(soa_resp)
        
        # Respond to ANY or CNAME queries
        if qtype in ('ANY', 'CNAME'):
            cname_resp = f"DATA	{qname}	{qclass}	CNAME	86400	{qid}	{TARGET_CNAME}
"
            stdout.write(cname_resp)
            
    stdout.write("END
")
    stdout.flush()

Make the script executable and restart PowerDNS:

chmod +x /etc/pdns/pdns-backend.py
systemctl restart pdns