Quickly add a reverse proxy via the Caddy Admin API

rproxy.sh

#!/bin/bash
# rproxy.sh - Quickly add a reverse proxy via the Caddy Admin API
# Usage: rproxy <UPSTREAM_ADDR> <LISTEN_ADDR>
# Example: rproxy localhost:3000 :8080
# SPDX-License-Identifier: MIT (https://ncurl.xyz/s/Kkn2DQsNR)

# 0. Check if jq is installed
if ! command -v jq &> /dev/null; then
    echo "Error: This script requires 'jq'. Please install jq first." >&2
    exit 1
fi

# 1. Check arguments
if [ "$#" -ne 2 ]; then
    echo "Usage: $0 <UPSTREAM_ADDR> <LISTEN_ADDR>" >&2
    echo "Example: $0 localhost:3000 :8080" >&2
    exit 1
fi

# Caddy Admin API address
CADDY_API="${CADDY_API:-localhost:2019}"

# Input arguments
UPSTREAM_ADDR="$1"
LISTEN_ADDR="$2"

# 2. Prepare variables
SERVER_ID="rproxy_${LISTEN_ADDR}" # Unique server ID (for idempotency)

# 3. Generate JSON Payload using jq
JSON_PAYLOAD=$(jq -n \
    --arg listen_addr "$LISTEN_ADDR" \
    --arg upstream_addr "$UPSTREAM_ADDR" \
    '{
      listen: [$listen_addr],
      routes: [
        {
          handle: [
            {
              handler: "reverse_proxy",
              upstreams: [ { dial: $upstream_addr } ]
            }
          ]
        }
      ]
    }'
)

# 4. Send request to Caddy Admin API
#    -s: silent, -f: fail-fast (exit on HTTP error)
OUTPUT=$(curl -vf -X POST \
    "http://${CADDY_API}/config/apps/http/servers/${SERVER_ID}" \
    -H "Content-Type: application/json" \
-d "$JSON_PAYLOAD" 2>&1)
CURL_EXIT_CODE=$?

# 5. Check curl's exit status
if [ $CURL_EXIT_CODE -eq 0 ]; then
    echo "Caddy proxy created: ${LISTEN_ADDR} -> ${UPSTREAM_ADDR} (ID: ${SERVER_ID})"
    elif [ $CURL_EXIT_CODE -eq 22 ]; then
    # Exit code 22 means HTTP error (e.g., 400, 404, 500)
    echo "Failure! Caddy API rejected the request (HTTP 4xx/5xx)." >&2
    echo "Run with 'curl -v' manually to see Caddy's error message." >&2
    echo "Error: $OUTPUT" >&2
    exit $CURL_EXIT_CODE
else
    # Other curl error (e.g., 7 - couldn't connect)
    echo "Failure! curl error $CURL_EXIT_CODE." >&2
    echo "Error: $OUTPUT" >&2
    exit $CURL_EXIT_CODE
fi