Initial implementation of a ddns script.

ddns.bash

@@ -0,0 +1,128 @@
+#!/usr/bin/env bash
+# This script runs a loop that continuously updates a DigitalOcean DNS record to
+# reflect this computer's current IP address. It uses an IP address mirror
+# service to discover the computer's current IP address and updates the DNS
+# record if the address is different.
+#
+# Args: None
+# Env:
+#   Required:
+#     DOMAIN:            The top level domain name (example.com)
+#     NAME:              The subdomain name (home)
+#     DIGIALOCEAN_TOKEN: A DigitalOcean personal access token with permission to
+#                        read, create, and update domain entries.
+#   Optional:
+#     DIGITALOCAEN_TOKEN_FILE: If set, DIGITALOCEAN_TOKEN will be read from this
+#                              file.
+#     SLEEP_INTERVAL:          The number of seconds to wait between updates.
+#                              Defaults to 60.
+
+set -euo pipefail
+[[ -v DEBUG ]] && set -x
+
+debug() {
+    echo "$@" 1>&2
+}
+
+die() {
+    debug "$@"
+    exit 1
+}
+
+(( $# == 0 )) || die "Got $# arguments, want 0"
+
+[[ -n "${DOMAIN:-}" ]] || die "DOMAIN not set"
+[[ -n "${NAME:-}" ]] || die "NAME not set"
+
+if [[ -f "${DIGITALOCEAN_TOKEN_FILE:-}" ]]; then
+    DIGITALOCEAN_TOKEN="$(cat "${DIGITALOCEAN_TOKEN_FILE}")"
+fi
+[[ -n "${DIGITALOCEAN_TOKEN:-}" ]] || die "DIGITALOCEAN_TOKEN not set"
+
+API_HOST="${API_HOST:-https://api.digitalocean.com/v2}"
+SLEEP_INTERVAL="${SLEEP_INTERVAL:-60}"
+IP_SERVICES=(
+    v4.ident.me
+    ifconfig.co
+    ifconfig.me
+    api.ipify.org
+)
+resolve_ip() {
+    for service in "${IP_SERVICES[@]}"; do
+        debug "Trying ${service}"
+        if curl -s "${service}"; then
+            return
+        fi
+    done
+    return 1
+}
+
+API="${API_HOST}/domains/${DOMAIN}/records"
+api_curl() {
+    curl -s --fail-with-body \
+        -H "Authorization: Bearer ${DIGITALOCEAN_TOKEN}" \
+        "$@"
+}
+
+run() {
+    local addr
+    if ! addr="$(resolve_ip)"; then
+        debug "Unable to resolve current IP."
+        return 1
+    fi
+
+    local record
+    if ! record="$(api_curl -X GET "${API}?type=A&name=${NAME}.${DOMAIN}" \
+        | jq ".domain_records[0] // empty")"; then
+
+        debug "Unable to discover current DNS record."
+        return 1
+    fi
+
+    if [[ -n "${record}" ]]; then
+        # Update existing record, if necessary.
+        local record_addr
+        if ! record_addr="$(jq -r '.data // empty' <<< "${record}")"; then
+            debug "Couldn't extract data from DNS record."
+            return 1
+        fi
+        if [[ "${record_addr}" == "${addr}" ]]; then
+            debug "DNS record has correct address."
+            return
+        fi
+
+        local record_id
+        if ! record_id="$(jq -r '.id // empty' <<< "${record}")"; then
+            debug "Couldn't extract id from DNS record."
+            return 1
+        fi
+        if [[ -z "${record_id}" ]]; then
+            debug "DNS record ID appears to be empty."
+            return 1
+        fi
+
+        local req
+        printf -v req '{"data": "%s", "ttl": %d}' "${addr}" "${SLEEP_INTERVAL}"
+        if ! api_curl -X PATCH "${API}/${record_id}" -d "${req}"; then
+            debug "Unable to update existing DNS record."
+            return 1
+        fi
+        echo # Add a newline for the curl output.
+    else
+        # Create new record.
+        local req
+        printf -v req '{"type": "A", "name": "%s", "data": "%s", "ttl": %d}' "${NAME}" "${addr}" "${SLEEP_INTERVAL}"
+        if ! api_curl -X POST "${API}" -d "${req}"; then
+            debug "Unable to create DNS record."
+            return 1
+        fi
+        echo # Add a newline for the curl output.
+    fi
+}
+
+while true; do
+    if ! run; then
+       debug "Attempt failed, trying again in ${SLEEP_INTERVAL} seconds."
+    fi
+    sleep "${SLEEP_INTERVAL}"
+done