Code

.gitignore

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+.env

.sample.env

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+EMAIL="my@mail.com"
+KEY="my_api_key" # found in cloudflare account settings
+ZONE="example.org"
+DNS_RECORD="some.example.org"

docker-compose.yml

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+version: '3'
+
+services:
+  updater:
+    build: .
+    restart: always
+    env_file: .env

dockerfile

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+FROM alpine:3.8
+
+ENV file /usr/local/bin/run.sh
+
+RUN apk add --no-cache --update curl grep bash
+
+RUN echo '*  *  *  *  * ${file}' > /etc/crontabs/root
+
+COPY ./run.sh ${file}
+RUN chmod +x ${file}
+
+CMD ["crond", "-l2", "-f"]

run.sh

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+#!/bin/bash
+
+# CHANGE THESE
+auth_email=${EMAIL}
+auth_key=${KEY}
+zone_name=${ZONE}
+record_name=${DNS_RECORD}
+
+# MAYBE CHANGE THESE
+ip=$(curl -s http://ipv4.icanhazip.com)
+ip_file="ip.txt"
+id_file="cloudflare.ids"
+log_file="cloudflare.log"
+
+# LOGGER
+log() {
+    if [ "$1" ]; then
+        echo -e "[$(date)] - $1" >> $log_file
+    fi
+}
+
+# SCRIPT START
+log "Check Initiated"
+
+if [ -f $ip_file ]; then
+    old_ip=$(cat $ip_file)
+    if [ $ip == $old_ip ]; then
+        echo "IP has not changed."
+        exit 0
+    fi
+fi
+
+if [ -f $id_file ] && [[ $(wc -l $id_file | cut -d " " -f 1) == 2 ]]; then
+    zone_identifier=$(head -1 $id_file)
+    record_identifier=$(tail -1 $id_file)
+else
+    zone_identifier=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones?name=$zone_name" -H "X-Auth-Email: $auth_email" -H "X-Auth-Key: $auth_key" -H "Content-Type: application/json" | grep -Po '(?<="id":")[^"]*' | head -1 )
+    record_identifier=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones/$zone_identifier/dns_records?name=$record_name" -H "X-Auth-Email: $auth_email" -H "X-Auth-Key: $auth_key" -H "Content-Type: application/json"  | grep -Po '(?<="id":")[^"]*')
+    echo "$zone_identifier" > $id_file
+    echo "$record_identifier" >> $id_file
+fi
+
+echo "Updating $zone_identifier, $record_identifier"
+
+update=$(curl -s -X PUT "https://api.cloudflare.com/client/v4/zones/$zone_identifier/dns_records/$record_identifier" -H "X-Auth-Email: $auth_email" -H "X-Auth-Key: $auth_key" -H "Content-Type: application/json" --data "{\"id\":\"$zone_identifier\",\"type\":\"A\",\"name\":\"$record_name\",\"content\":\"$ip\"}")
+
+if [[ $update == *"\"success\":false"* ]]; then
+    message="API UPDATE FAILED. DUMPING RESULTS:\n$update"
+    log "$message"
+    echo -e "$message"
+    exit 1 
+else
+    message="IP changed to: $ip"
+    echo "$ip" > $ip_file
+    log "$message"
+    echo "$message"
+fi