Configure Kafka TLS Encryption

By default, Redpanda data is sent unencrypted. A security best practice is to enable encryption with TLS or mTLS.

  • Transport Layer Security (TLS), previously SSL, provides encryption for client-server communication. A server certificate prevents third parties from accessing data transferred between the client and server. By default, Redpanda clusters accept connections from clients using TLS version 1.2 or later, but this value is configurable.

  • mTLS, or 2-way TLS, is a protocol that authenticates both the server and the client. In addition to the server certificate required in TLS, mTLS also requires the client to give a certificate. This involves more overhead to implement, but it can be useful for environments that require additional security and only have a small number of verified clients.

For each Redpanda broker, you must specify the:

  • key file (broker.key)

  • certificate file (broker.crt)

  • truststore file (ca.crt).

Each broker has its own broker.key and broker.crt, but all brokers can have the same ca.crt.

If you enable TLS encryption, you can also specify a certificate revocation list (ca.crl) so that Redpanda can check and reject connections from entities using certificates already revoked by a certificate authority (CA). All brokers can have the same ca.crl. The file must contain a single, concatenated list of certificate revocation lists (CRLs) for all issuing certificates in the truststore file.

Prerequisites

TLS certificates are necessary for encryption. You can use your own certificates, either self-signed or issued by a trusted CA.

Create a local CA for self-signed certificates

This step is required if you want to generate multiple certificates all signed by the same root; for example, you want to use mTLS but issue different certificates to multiple Redpanda brokers and clients.

To generate a self-signed certificate in a single command:

openssl req -new -newkey rsa:4096 -days 365 -nodes -x509 -keyout broker.key -out broker.crt -subj "/CN=redpanda" -addext "subjectAltName = DNS:localhost, IP: 127.0.0.1"

1. Create CA configuration file (ca.cnf)

Edit the distinguished_name section with your own organization details. For default_md, sha256 is the minimum message digest level. The subjectAltName must be accurate for the broker’s certificate.

ca.cnf
[ ca ]
default_ca = CA_default

[ CA_default ]
default_days    = 365
database        = index.txt
serial          = serial.txt
default_md      = sha256
copy_extensions = copy
unique_subject  = no
policy          = signing_policy
[ signing_policy ]
organizationName = supplied
commonName       = optional

# Used to create the CA certificate.
[ req ]
prompt             = no
distinguished_name = distinguished_name
x509_extensions    = extensions

[ distinguished_name ]
organizationName = Redpanda
commonName       = Redpanda CA

[ extensions ]
keyUsage         = critical,digitalSignature,nonRepudiation,keyEncipherment,keyCertSign
basicConstraints = critical,CA:true,pathlen:1

# Common policy for nodes and users.
[ signing_policy ]
organizationName = supplied
commonName       = optional

Create a CA key to self-sign certificates:

openssl genrsa -out ca.key 2048
chmod 400 ca.key

Create a public certificate for the CA:

openssl req -new -x509 -config ca.cnf -key ca.key -days 365 -batch -out ca.crt

where:

Inputs Description

-new

New request.

-x509

Create an X.509 certificate, instead of a certificate signing request (CSR).

-config ca.cnf

Configuration file to use when generating certificates (created above).

-key ca.key

Private key of the CA (created above).

-days 365

Number of days signed certificates are valid.

-batch

Batch mode, where certificates are certified automatically.
Output Description

-out ca.crt

The public key certificate of the CA.

Create certificate signing requests

This step creates the certificate signing request for the CA to extend trust over the broker’s certificates.

1. Create broker configuration file (broker.cnf)

A subject alternative name (SAN) indicates all domain names and IP addresses secured by the certificate. Depending on the address the client uses to connect to Redpanda, you might need to create a CNF file for each broker to modify the alt_names section with organizational details. For production usage, edit alt_names with DNS resolutions and/or the IP addresses.

broker.cnf
[ req ]
prompt             = no
distinguished_name = distinguished_name
req_extensions     = extensions

[ distinguished_name ]
organizationName = Redpanda

[ extensions ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = localhost
DNS.2 = redpanda
DNS.3 = console
DNS.4 = connect
DNS.5 = ec2-3-15-15-272.us-east-2.compute.amazonaws.com
IP.1  = 10.0.8.1

You could configure alternative names with a single version of broker.key/broker.crt, as long as you update the certificate for all brokers in the cluster any time you edit an entry. For example:

[ alt_names ]
DNS.1 = broker1.example.com
DNS.2 = broker2.example.com
DNS.3 = broker3.example.com

Additionally, you can configure alternative names using the public or private IP addresses of all your brokers. For example:

[ alt_names ]
IP.1 = 10.0.8.1
IP.2 = 10.0.8.2
IP.3 = 10.0.8.3

2. Generate broker private key (broker.key)

Generate a 2048-bit RSA private key for brokers:

openssl genrsa -out broker.key 2048

where:

Output Description

-out broker.key

The private key certificate for the broker.

3. Generate certificate signing request

Before signing certificates, you must run the following command to generate the broker’s certificate signing request:

openssl req -new -key broker.key -out broker.csr -nodes -config broker.cnf

where:

Inputs Description

-req

Input is a certificate request. Sign and output.

-signkey ca.key

Private key of the CA (created above).

-days 365

Number of days signed certificates are valid.

-extfile broker.cnf

Configuration file for CA.

-extensions extensions

Section in broker.cnf to use when applying extensions.

-in broker.csr

Broker certificate signing request (CSR generated above).
Output Description

-out broker.crt

The signed public key certificate for the broker.

4. Sign certificates

Sign the certificate with the CA signature:

touch index.txt
echo '01' > serial.txt
openssl ca -config ca.cnf -keyfile ca.key -cert ca.crt -extensions extensions -in broker.csr -out broker.crt -outdir . -batch

chown redpanda:redpanda broker.key broker.crt ca.crt
chmod 400 broker.key broker.crt ca.crt

If generated by a corporate CA, these certificate signing requests must be signed with the following extensions:

keyUsage         = critical,digitalSignature,keyEncipherment
extendedKeyUsage = serverAuth,clientAuth

Configure TLS

To configure TLS, in redpanda.yaml, enter:

redpanda.yaml
redpanda:
  rpc_server_tls: {}
  kafka_api:
    - address: 0.0.0.0
      port: 9092
      name: tls_listener
  kafka_api_tls:
    - name: tls_listener
      key_file: broker.key
      cert_file: broker.crt
      truststore_file: ca.crt
      crl_file: ca.crl # Optional
      enabled: true
      require_client_auth: false
  admin_api_tls: []
pandaproxy:
  pandaproxy_api_tls: []
schema_registry:
  schema_registry_api_tls: []

The following files must be readable by Redpanda, either through 444 permissions or chown to Redpanda with 400 permissions:

  • broker.crt

  • broker.key

  • ca.crt

  • ca.crl

Because the keys and certificates are only read at startup, you must restart Redpanda services after updating redpanda.yaml. TLS-related changes to redpanda.yaml will not be known to Redpanda until after this restart:

systemctl restart redpanda

If you replace a working ca.crl file with a file that contains an invalid certificate revocation list, such as an unsigned list, Redpanda will reject all connections until you either:

  • Replace the file.

  • Remove the crl_file: ca.crl line from redpanda.yaml and restart Redpanda.

To set the RPC port to encrypt replication, add:

redpanda.yaml
redpanda:
  rpc_server_tls:
    enabled: true
    require_client_auth: false
    key_file: broker.key
    cert_file: broker.crt
    truststore_file: ca.crt
    crl_file: ca.crl # Optional

Schema Registry and HTTP Proxy connect to Redpanda over the Kafka API. If you configure a TLS listener for the Kafka API, you must add schema_registry_client::broker_tls and pandaproxy_client::broker_tls. All APIs, except the internal RPC port, support multiple listeners. See:

Manage the minimum TLS version

Redpanda sets the minimum TLS version for all clusters to 1.2, using the tls_min_version cluster configuration property. This prevents client applications from negotiating a downgrade to the TLS version when they make a connection to a Redpanda cluster.

You can update the minimum TLS version of your clusters to v1.0, v1.1 or v1.3 using rpk. Replace the placeholder in brackets.

rpk cluster config set tls_min_version <version-number>

You must restart Redpanda for the new setting to take effect:

systemctl restart redpanda

Configure mTLS

To enable mTLS, add require_client_auth set to true.

For example, for the Kafka API, in redpanda.yaml, enter:

redpanda.yaml
redpanda:
  kafka_api:
    - address: 0.0.0.0
      port: 9092
      name: mtls_listener
  kafka_api_tls:
    - name: mtls_listener
      key_file: mtls_broker.key
      cert_file: mtls_broker.crt
      truststore_file: mtls_ca.crt
      enabled: true
      require_client_auth: true

See also: Configure Listeners

Configure mTLS for a Kafka API listener

To enable mTLS for a Kafka API listener, edit redpanda.yaml:

redpanda.yaml
redpanda:
  kafka_api:
  - name: internal
    address: 0.0.0.0
    port: 9092

  advertised_kafka_api:
    - name: internal
      address: <port-clients-connect-to>
    port: 9092

  kafka_api_tls:
  - name: internal
    enabled: true
    require_client_auth: true
    cert_file: <path-to-PEM-formatted-cert-file>
    key_file: <path-to-PEM-formatted-key-file>
    truststore_file: <path-to-PEM-formatted-CA-file>

  • Remember to replace placeholders in brackets.

  • kafka_api is the listener declaration. This name can have any value.

  • advertised_kafka_api is the advertised listener. This name should match the name of a declared listener. This address is the host name clients use to connect to the broker.

  • kafka_api_tls is the listener’s TLS configuration. This name must match the corresponding listener’s name.

See also: Configure Listeners

Use rpk with TLS

If you’re using rpk to interact with the Kafka API using mTLS identity (for example, to manage topics or messages), pass the --tls-key, --tls-cert, and --tls-truststore flags to authenticate.

To create a new topic called test-topic, run:

 rpk topic create test-topic \
--tls-key <path-to-PEM-formatted-key-file> \
--tls-cert <path-to-PEM-formatted-cert-file> \
--tls-truststore <path-to-PEM-formatted-CA-file>

Replace placeholders in brackets.

To check the configuration of the topic, run:

rpk topic describe test-topic <tls-flags-from-above>

To interact with the Admin API (for example, to manage users), pass the --admin-api-tls-key, --admin-api-tls-cert, and --admin-api-tls-truststore flags.

By default, rpk connects to localhost:9092 for Kafka protocol commands. If you’re connecting to a remote broker or if you configured your local broker differently, use the -X brokers=<address:port> flag.

Monitor TLS certificates

Redpanda exposes several metrics to help administrators manage their installed certificates. When queried, these metrics list details for all resources that have an installed certificate. This may include APIs, storage, or other assets. These metrics also support labels so that you can more readily report statistics on single resources.

Configuring alerts on these metrics is a critical tool for managing certificate expiration and avoiding surprise outages. The public metrics reference contains a full list of available TLS metrics. You can refer to the monitor Redpanda guide for full details on configuring Prometheus to monitor these metrics. This guide also explains how to create a Grafana dashboard for visualizations and alerting.

Alternatively, you can choose to specify a certificate revocation list to reject connections from entities using certificates already revoked by a certificate authority.

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