Resolve DNS with exponential backoff

resolve_dns_with_backoff.sh

#!/bin/bash
# vim: ai:ts=8:sw=8:noet
# set -eufo pipefail
export SHELLOPTS # propagate set to children by default
IFS=$'\t\n'

# Performs a DNS resolution  and waits until the answer has a non-empty response
function resolve_dns_with_backoff {
    local timeout=${DNS_RESOLUTION_TIMEOUT-5}
    local domain=${1}
    local attempt=0
    local backoff=1
    local now
    local end
    now=$(date +%s)
    end=$((now + timeout))

    while [[ ${now} < ${end} ]]
    do
        response=$(dig +short "${domain}")
        if [ -n "${response}" ]; then
            echo "DNS Response is ${response}"
            return 0
        fi
        echo "Attempt $attempt - DNS Response was empty! Retrying in $backoff seconds.." 1>&2
        sleep "${backoff}"
        attempt=$(( attempt + 1 ))
        backoff=$(( backoff * 2 ))
        now=$(date +%s)
    done

    return 1
}