kafka producer does not throw exception when broker is down

Created a cluster with two brokers using same zookeeper and trying to produce message to a topic whose details are as below.

When the producer sets acks="all" or -1,min.insync.replicas="2", it is supposed to receive acknowledgement from the brokers(leaders and replicas) but when one broker is shut manually while it is producing, it is making no difference to the kafka producer even when acks=”all” can someone explain the reason for this weird behavior?

brokers are on 9091,9092.

acks = -1
batch.size = 16384
bootstrap.servers = [localhost:9092]
buffer.memory = 33554432
client.dns.lookup = use_all_dns_ips
client.id = producer-1
compression.type = none
connections.max.idle.ms = 540000
delivery.timeout.ms = 120000
enable.idempotence = false
interceptor.classes = []
internal.auto.downgrade.txn.commit = false
key.serializer = class org.apache.kafka.common.serialization.StringSerializer
linger.ms = 0
max.block.ms = 60000
max.in.flight.requests.per.connection = 5
max.request.size = 1048576
metadata.max.age.ms = 300000
metadata.max.idle.ms = 300000
metric.reporters = []
metrics.num.samples = 2
metrics.recording.level = INFO
metrics.sample.window.ms = 30000
partitioner.class = class org.apache.kafka.clients.producer.internals.DefaultPartitioner
receive.buffer.bytes = 32768
reconnect.backoff.max.ms = 1000
reconnect.backoff.ms = 50
request.timeout.ms = 30000
retries = 2147483647
retry.backoff.ms = 100
sasl.client.callback.handler.class = null
sasl.jaas.config = null
sasl.kerberos.kinit.cmd = /usr/bin/kinit
sasl.kerberos.min.time.before.relogin = 60000
sasl.kerberos.service.name = null
sasl.kerberos.ticket.renew.jitter = 0.05
sasl.kerberos.ticket.renew.window.factor = 0.8
sasl.login.callback.handler.class = null
sasl.login.class = null
sasl.login.refresh.buffer.seconds = 300
sasl.login.refresh.min.period.seconds = 60
sasl.login.refresh.window.factor = 0.8
sasl.login.refresh.window.jitter = 0.05
sasl.mechanism = GSSAPI
security.protocol = PLAINTEXT
security.providers = null
send.buffer.bytes = 131072
ssl.cipher.suites = null
ssl.enabled.protocols = [TLSv1.2]
ssl.endpoint.identification.algorithm = https
ssl.engine.factory.class = null
ssl.key.password = null
ssl.keymanager.algorithm = SunX509
ssl.keystore.location = null
ssl.keystore.password = null
ssl.keystore.type = JKS
ssl.protocol = TLSv1.2
ssl.provider = null
ssl.secure.random.implementation = null
ssl.trustmanager.algorithm = PKIX
ssl.truststore.location = null
ssl.truststore.password = null
ssl.truststore.type = JKS
transaction.timeout.ms = 60000
transactional.id = null
value.serializer = class org.apache.kafka.common.serialization.StringSerializer

Below is the source code for the kafka producer

public static  void main(String k[]) {
    Properties prop=new Properties();
    prop.setProperty(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG,"localhost:9092");
    prop.setProperty(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());
    prop.setProperty(ProducerConfig.ACKS_CONFIG,"all");
    prop.setProperty("min.insync.replicas", "2");
    prop.setProperty(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());
    KafkaProducer<String,String> producer=new KafkaProducer<>(prop);
    ProducerRecord<String,String> rec=new ProducerRecord<String,String>("clust_topic","123");
while(true) {
    producer.send(rec, new Callback() {

        @Override
        public void onCompletion(RecordMetadata rm, Exception arg1) {
            System.out.println(arg1);
            if(arg1!=null)
              System.out.println(arg1);
            else
                System.out.println(rm.topic()+" "+rm.partition()+" "+rm.offset()+" ");      
        }       
    });
  }
}

Answer

ack=all means that it requires ack from all in-sync replicas, not from all replicas (refer to documentation)