Everday syslog-ng: How to configure syslog-ng Kafka destination to use Kerberos

Hello guys,

Now I just want to write something interesting about my favorite logging application called syslog-ng.


  • Active Kerberos server
  • Active Apache Kafka server configured to use Kerberos
  • The Kerberos client libs (krb5-user krb5-config) are installed and configured on the host where syslog-ng is running
  • syslog-ng OSE 3.12 or newer
  • or syslog-ng Premium Edition 7.0.5 or newer
  • Java Cryptography Extension (JCE): To use Kerberos, syslog-ng needs this Java extension. You should download and install it to your computer where syslog-ng runs.

In the first scenario, I will configure syslog-ng to use Kerberos with SASL_PLAINTEXT authentication, in the second part, Kerberos with SSL.

Syslog-ng configuration

First of all we need a syslog-ng configuration. Here is mine (the embedded configs are detailed below):

@version: 3.12
@module “mod-java”
@include “scl.conf”
options {
jvm_options(“-Djava.security.auth.login.config=/home/pzolee/install/configs/kafkakerberos/client.jaas -Djava.security.krb5.conf=/etc/krb5.conf -Dlog4j.configuration=file:/home/pzolee/install/configs/kafkakerberos/log4.properties”);

source s_network_5acd1de3c3494308820dd80525d0a1aa {

destination d_kafka_e0fb1bbb06d345f4ba3770b4eecc4a8a {


log {

It just contains a simple network (tcp) source where the logs are coming, and a Kafka destination where the logs are forwarded. For the options of Kafka destination, read the documentation.

The client.jaas file contains the required parts for Kerberos:

cat client.jaas
KafkaClient {
com.sun.security.auth.module.Krb5LoginModule required refreshKrb5Config=true useKeyTab=true keyTab=”/home/pzolee/install/configs/kafkakerberos/client.keytab” storeKey=true principal=”client/thor.mydomain@SYSLOG-NG.MYDOMAIN”;};

Keytab file

Because syslog-ng runs as a daemon without interactive user login, we want to use keytab file instead of manually initialize Kerberos and typing the password.

So generate a Kerberos keytab file for syslog-ng. Here is the example of my keytab file:

klist -kte /home/pzolee/install/configs/kafkakerberos/client.keytab
Keytab name: FILE:/home/pzolee/install/configs/kafkakerberos/client.keytab
KVNO Timestamp           Principal

—- ——————- ——————————————————

1 2017-09-26 15:18:23 client/thor.mydomain@SYSLOG-NG.MYDOMAIN(aes256-cts-hmac-sha1-96)

Don’t forget, Kerberos checks the FQDN in the principal, so the hostname should be correct.
Properties files

We need a Kafka producer properties files for syslog-ng with the following content:

cat /home/pzolee/install/configs/kafkakerberos/producer.properties

For bootstrap.servers you should use your Kafka server and for sasl.kerberos.service.name the same name that is configured in the server.properties file in the Kafka server.

And another one for log4j to see some debug messages

cat /home/pzolee/install/configs/kafkakerberos/log4.properties

Now start syslog-ng:

sbin/syslog-ng -Fevd

[2017-09-28T10:24:08.306159] syslog-ng starting up; version=’3.11.1′
[2017-09-28T10:24:08.341826] ProducerConfig values: \x0a acks = 1\x0a batch.size = 16384\x0a bootstrap.servers = [thor.mydomain:9092]\x0a buffer.memory = 33554432\x0a client.id = \x0a compression.type = none\x0a connections.max.idle.ms = 540000\x0a enable.idempotence = false\x0a interceptor.classes = null\x0a key.serializer = class org.apache.kafka.common.serialization.StringSerializer\x0a linger.ms = 0\x0a max.block.ms = 60000\x0a max.in.flight.requests.per.connection = 5\x0a max.request.size = 1048576\x0a metadata.max.age.ms = 300000\x0a metric.reporters = []\x0a metrics.num.samples = 2\x0a metrics.recording.level = INFO\x0a metrics.sample.window.ms = 30000\x0a partitioner.class = class org.apache.kafka.clients.producer.internals.DefaultPartitioner\x0a receive.buffer.bytes = 32768\x0a reconnect.backoff.max.ms = 1000\x0a reconnect.backoff.ms = 50\x0a request.timeout.ms = 30000\x0a retries = 0\x0a retry.backoff.ms = 100\x0a sasl.jaas.config = null\x0a sasl.kerberos.kinit.cmd = /usr/bin/kinit\x0a sasl.kerberos.min.time.before.relogin = 60000\x0a sasl.kerberos.service.name = kafka\x0a sasl.kerberos.ticket.renew.jitter = 0.05\x0a sasl.kerberos.ticket.renew.window.factor = 0.8\x0a sasl.mechanism = GSSAPI\x0a security.protocol = SASL_PLAINTEXT\x0a send.buffer.bytes = 131072\x0a ssl.cipher.suites = null\x0a ssl.enabled.protocols = [TLSv1.2, TLSv1.1, TLSv1]\x0a ssl.endpoint.identification.algorithm = null\x0a ssl.key.password = null\x0a ssl.keymanager.algorithm = SunX509\x0a ssl.keystore.location = null\x0a ssl.keystore.password = null\x0a ssl.keystore.type = JKS\x0a ssl.protocol = TLS\x0a ssl.provider = null\x0a ssl.secure.random.implementation = null\x0a ssl.trustmanager.algorithm = PKIX\x0a ssl.truststore.location = null\x0a ssl.truststore.password = null\x0a ssl.truststore.type = JKS\x0a transaction.timeout.ms = 60000\x0a transactional.id = null\x0a value.serializer = class org.apache.kafka.common.serialization.StringSerializer\x0a;
[2017-09-28T10:24:08.713300] Successfully logged in.;
[2017-09-28T10:24:08.716513] [Principal=client/thor.mydomain@SYSLOG-NG.MYDOMAIN]: TGT refresh thread started.;
[2017-09-28T10:24:08.719814] [Principal=client/thor.mydomain@SYSLOG-NG.MYDOMAIN]: TGT valid starting at: Thu Sep 28 10:24:21 CEST 2017;
[2017-09-28T10:24:08.720000] [Principal=client/thor.mydomain@SYSLOG-NG.MYDOMAIN]: TGT expires: Thu Sep 28 20:24:21 CEST 2017;
[2017-09-28T10:24:08.720146] [Principal=client/thor.mydomain@SYSLOG-NG.MYDOMAIN]: TGT refresh sleeping until: Thu Sep 28 18:29:04 CEST 2017;

As you can see, syslog-ng could log in to Kafka using kerberos.

Configuring syslog-ng Kafka destination with Kerberos and SSL


  • Kafka broker is configured to use Kerberos with SSL

You only need a few minor changes in producer.properties file:

cat /home/pzolee/install/configs/kafkakerberos/producer.properties

You only have to change the security.protocol from SASL_PLAINTEXT to SASL_SSL and provide the keystore and truststore paths and passwords.

If you want to see the ssl logs, add “-Djavax.net.debug=all” to the jvm_options.