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Blog
Mar 6, 2023
7 min read

Understanding and Configuring mTLS in Apache Pulsar

Zixuan Liu
Software Engineer, StreamNative
Understanding and Configuring mTLS in Apache Pulsar

Apache Pulsar is an open-source messaging and streaming system that provides high throughput and low latency for enterprises. To power use cases requiring strict security controls, it supports a variety of popular security frameworks, like TLS, mTLS, Athenz, Kerberos, JWT, and OAuth2.0. In this blog, I will introduce how to configure mTLS encryption and authentication in Apache Pulsar.

I will not dive deep into each security mechanism in Pulsar as this blog is focused on mTLS configuration in Pulsar. That said, I do think gaining a basic understanding of them is very important for you to choose the right security policy for your organization. If you want to know more about available security combinations in Pulsar, read the blog A Practical Guide to Enterprise-Grade Security in Apache Pulsar.

What is mTLS?

Before I talk about mTLS, let me explain TLS and how it works at a cursory level. Transport Layer Security (TLS), formerly known as SSL, is a cryptographic protocol to secure communications between two entities over a network. It guarantees data integrity and confidentiality with a public key, a private key, and a TLS certificate. Only the private key can decrypt the data encrypted by the public key. The certificate, which contains the public key, is used to verify the identity of the server.

Compared with TLS, Mutual TLS (mTLS) is a more secure protocol as it uses two-way authentication to make sure both entities are who they claim to be. As an extension of TLS, mTLS allows both the client and the server to use the certificates of each side to confirm their identities. This way, only trusted entities can have data access.

Figure 1. Mutual TLS

Why do I need mTLS in Pulsar?

Typically, mTLS is the preferred solution for configuring encryption and authentication on the cloud. As it ensures both the client and the server can verify their identities, it provides an extra layer of security.

By default, there is no security policy applied in Pulsar. Clients communicate with Pulsar in plain text. To protect sensitive information against attackers and eavesdroppers, you can use mTLS to encrypt your data streams in transit. Additionally, Pulsar provides a built-in TLS authentication plugin that can identify the client through the common name in the certificate.

Configuring mTLS in Pulsar

To use mTLS, you need some configurations both on the client and on the server. When configuring the server, you may need to set some parameters for Pulsar proxies as well depending on your deployment. Before I introduce how to configure mTLS connections, let me briefly explain why you may need the proxy layer. I believe this contributes to your understanding of how encryption and authentication work in Pulsar.

There are two typical ways to connect to Pulsar depending on how your cluster is deployed. You can either connect to Pulsar brokers directly or send requests to the proxy layer, which routes traffic to brokers. The proxy layer is optional and is commonly used in environments where external requests cannot be directly sent to brokers. For example, you can use proxy Pods to serve as the gateway if your Pulsar cluster is deployed on Kubernetes.

Now that you have a basic understanding of how clients can connect to Pulsar, let’s see how to configure mTLS for transport encryption and identity authentication respectively.

mTLS encryption

Transport encryption means that you encrypt your data before it travels across the network. As it gets decrypted on the server side, your data remains secure during transmission. To use mTLS encryption, you can set related parameters on the broker, the proxy, and the client. Note that you must create the following certificates and keys beforehand:

  • CA certificate
  • Server’s certificate and private key
  • Client’s certificate and private key

For more information on certificates and keys, see the Pulsar documentation. When you have them ready, refer to the configurations below for each component.

Broker configurations

Add the following configurations to broker.conf to enable mTLS.

# TLS ports
brokerServicePortTls=6651
webServicePortTls=8081

# CA certificate
tlsTrustCertsFilePath=/path/to/ca.cert.pem
# Server certificate
tlsCertificateFilePath=/path/to/broker.cert.pem
# Private key for the server
tlsKeyFilePath=/path/to/broker.key-pk8.pem

# Enable mTLS
tlsRequireTrustedClientCertOnConnect=true

# Configure TLS for the internal client to connect to the broker
brokerClientTlsEnabled=true
brokerClientTrustCertsFilePath=/path/to/ca.cert.pem
brokerClientCertificateFilePath=/path/to/client.cert.pem
brokerClientKeyFilePath=/path/to/client.key-pk8.pem

Proxy configurations

Add the following configurations to proxy.conf to enable mTLS.

# TLS ports
servicePortTls=6651
webServicePortTls=8081

# CA certificate
tlsTrustCertsFilePath=/path/to/ca.cert.pem
# Server certificate
tlsCertificateFilePath=/path/to/proxy.cert.pem
# Private key for the server
tlsKeyFilePath=/path/to/proxy.key-pk8.pem

# Enable mTLS
tlsRequireTrustedClientCertOnConnect=true

# Configure TLS for the internal client to connect to the broker
tlsEnabledWithBroker=true
brokerClientTrustCertsFilePath=/path/to/ca.cert.pem
brokerClientCertificateFilePath=/path/to/client.cert.pem
brokerClientKeyFilePath=/path/to/client.key-pk8.pem

CLI tools

Add the following configurations to client.conf to enable mTLS.

webServiceUrl=https://localhost:8081/
brokerServiceUrl=pulsar+ssl://localhost:6651/
authPlugin=org.apache.pulsar.client.impl.auth.AuthenticationTls
authParams=tlsCertFile:/path/to/client.cert.pem,tlsKeyFile:/path/to/client.key-pk8.pem

Client code examples (Java)

PulsarAdmin admin = PulsarAdmin.builder().serviceHttpUrl("https://localhost:8081")
       .tlsTrustCertsFilePath("/path/to/ca.cert.pem")
       .tlsKeyFilePath("/path/to/client.key-pk8.pem")
       .tlsCertificateFilePath("/path/to/client.cert.pem")
       .build();

PulsarClient client = PulsarClient.builder().serviceUrl("pulsar+ssl://localhost:6651")
       .tlsTrustCertsFilePath("/path/to/ca.cert.pem")
       .tlsKeyFilePath("/path/to/client.key-pk8.pem")
       .tlsCertificateFilePath("/path/to/client.cert.pem")
       .build();

mTLS authentication

Authentication refers to the process of verifying the identity of requesters using their credentials. To use mTLS authentication, you can set related parameters on the broker, the proxy, and the client. Note that you must create the following certificates and keys beforehand:

  • CA certificate
  • Server’s certificate and private key
  • Client’s certificate and private key

When you have them ready, refer to the configurations below for each component.

Broker configurations

Add the following configurations to broker.conf to enable mTLS.

# TLS ports
brokerServicePortTls=6651
webServicePortTls=8081

# CA certificate
tlsTrustCertsFilePath=/path/to/ca.cert.pem
# Server certificate
tlsCertificateFilePath=/path/to/broker.cert.pem
# Private key for the server
tlsKeyFilePath=/path/to/broker.key-pk8.pem

# Enable mTLS
tlsRequireTrustedClientCertOnConnect=true

# Enable authentication
authenticationEnabled=true
# Set the TLS authentication plugin
authenticationProviders=org.apache.pulsar.broker.authentication.AuthenticationProviderTls

# Configure TLS for the internal client to connect to the broker
brokerClientTlsEnabled=true
brokerClientTrustCertsFilePath=/path/to/ca.cert.pem
brokerClientAuthenticationPlugin=org.apache.pulsar.client.impl.auth.AuthenticationTls
brokerClientAuthenticationParameters={"tlsCertFile":"/path/to/client.cert.pem","tlsKeyFile":"/path/to/client.key-pk8.pem"}

Proxy configurations

Add the following configurations to proxy.conf to enable mTLS.

# TLS ports
servicePortTls=6651
webServicePortTls=8081

# CA certificate
tlsTrustCertsFilePath=/path/to/ca.cert.pem
# Server certificate
tlsCertificateFilePath=/path/to/proxy.cert.pem
# Private key for the server
tlsKeyFilePath=/path/to/proxy.key-pk8.pem

# Enable mTLS
tlsRequireTrustedClientCertOnConnect=true

# Enable authentication
authenticationEnabled=true
# Set the TLS authentication plugin
authenticationProviders=org.apache.pulsar.broker.authentication.AuthenticationProviderTls

# Configure TLS for the internal client to connect to the broker
tlsEnabledWithBroker=true
brokerClientTrustCertsFilePath=/path/to/ca.cert.pem
brokerClientAuthenticationPlugin=org.apache.pulsar.client.impl.auth.AuthenticationTls
brokerClientAuthenticationParameters={"tlsCertFile":"/path/to/client.cert.pem","tlsKeyFile":"/path/to/client.key-pk8.pem"}

CLI tools

Add the following configurations to client.conf to use mTLS.

authPlugin=org.apache.pulsar.client.impl.auth.AuthenticationTls
authParams=tlsCertFile:/path/to/client.cert.pem,tlsKeyFile:/path/to/client.key-pk8.pem

Client code examples (Java)

Authentication tlsAuth = new AuthenticationTls("/path/to/client.cert.pem", "/path/to/client.key-pk8.pem");

PulsarAdmin admin = PulsarAdmin.builder().serviceHttpUrl("pulsar+ssl://localhost:6651")
       .tlsTrustCertsFilePath("/path/to/ca.cert.pem")
       .authentication(tlsAuth)
       .build();

PulsarClient client = PulsarClient.builder().serviceUrl("https://localhost:8081")
       .tlsTrustCertsFilePath("/path/to/ca.cert.pem")
       .authentication(tlsAuth)
       .build();

Conclusion

mTLS is an ideal solution for securing service-to-service communications for modern applications. That said, the authentication process itself requires some CPU resources, which means your cluster performance can be impacted. In the ever-changing cybersecurity field, I believe there is no one-size-fits-all solution and we need to have a flexible security policy based on the actual needs. This also means we need to make some trade-offs under certain circumstances. For example, in a “Zero Trust” environment, I suggest you enable mTLS for all connections so that every component on the network needs authentication to gain data access. When the connection between the proxy and the broker is trusted, you can only configure mTLS on the proxy layer for better CPU utilization.

More on Apache Pulsar

Pulsar has become one of the most active Apache projects over the past few years, with a vibrant community driving innovation and improvements to the project. Check out the following resources to learn more about Pulsar.

Zixuan Liu
Zixuan Liu is a software engineer at StreamNative. He mainly contributes to Apache Pulsar and Pulsarctl, focusing on the security field.

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