Retry name lookup for kubernetes and docker swarm environment (#4800)

Wait for remote hosts to resolve instead of failing on first host
resolution error, when running in Kubernetes or Docker environment.

Note that

- Waiting is based on exponential back-off mechanism
- If run as a binary, server fails if remote host is not resolvable

This is needed because in orchestration platforms like Kubernetes, remote
hosts are started sequentially and all the hosts are not up initially,
though they are expected to come up in a short time frame
It is difficult to identify a cap on the waiting time due to
non-deterministic nature of infrastructure platforms, so the server waits
infinitely for the hosts to come up, while logging the error messages to
the console.

Fixes: https://github.com/minio/minio/issues/4669

buildscripts/docker-entrypoint.sh

@@ -22,41 +22,6 @@ if [ "${1}" != "minio" ]; then
     fi
 fi
 
-# Wait for all the hosts to come online and have
-# their DNS entries populated properly.
-docker_wait_hosts() {
-    hosts="$@"
-    num_hosts=0
-    # Count number of hosts in arguments.
-    for host in $hosts; do
-        [ $(echo "$host" | grep -E "^http") ] || continue
-        num_hosts=$((num_hosts+1))
-    done
-    if [ $num_hosts -gt 0 ]; then
-        echo -n "Waiting for all hosts to resolve..."
-        while true; do
-            x=0
-            for host in $hosts; do
-                [ $(echo "$host" | grep -E "^http") ] || continue
-                # Extract the domain.
-                host=$(echo $host | sed -e 's/^http[s]\?:\/\/\([^\/]\+\).*/\1/')
-                echo -n .
-                val=$(ping -c 1 $host 2>/dev/null)
-                if [ $? != 0 ]; then
-                    echo "Failed to lookup $host"
-                    continue
-                fi
-                x=$((x+1))
-            done
-            # Provided hosts same as successful hosts, should break out.
-            test $x -eq $num_hosts && break
-            echo "Failed to resolve hosts.. retrying after 1 second."
-            sleep 1
-        done
-        echo "All hosts are resolving proceeding to initialize Minio."
-    fi
-}
-
 ## Look for docker secrets in default documented location.
 docker_secrets_env() {
     local MINIO_ACCESS_KEY_FILE="/run/secrets/access_key"
@@ -75,7 +40,4 @@ docker_secrets_env() {
 ## Set access env from secrets if necessary.
 docker_secrets_env
 
-## Wait for all the hosts to come online.
-docker_wait_hosts "$@"
-
 exec "$@"