Configuring TLS certificates

TLS is configured in opensearch.yml. Certificates are used to secure transport-layer traffic (node-to-node communication within your cluster) and REST-layer traffic (communication between a client and a node within your cluster). TLS is optional for the REST layer and mandatory for the transport layer.

You can find an example configuration template with all options on GitHub.

X.509 PEM certificates and PKCS #8 keys

The following tables contain the settings you can use to configure the location of your PEM certificates and private keys.

Transport layer TLS

REST layer TLS

Keystore and truststore files

As an alternative to certificates and private keys in PEM format, you can instead use keystore and truststore files in JKS or PKCS12/PFX format. For the Security plugin to operate, you need certificates and private keys.

The following settings configure the location and password of your keystore and truststore files. If you want, you can use different keystore and truststore files for the REST and the transport layer.

Transport layer TLS

REST layer TLS

Separate client and server certificates for transport layer TLS

By default, transport layer TLS certificates need to be configured as both the client (TLS Web Client Authentication) and server (TLS Web Server Authentication) in the certificate’s Extended Key Usage section because the nodes using the TLS certificates assume the responsibility of serving and receiving the communication requests internally. If you want to use separate certificates for the client and server, add the plugins.security.ssl.transport.extended_key_usage_enabled: true setting to opensearch.yml. Next, configure the settings outlined in the separate client and server X.509 PEM certificates and PKCS #8 keys or separate client and server keystore and truststore files sections.

Separate client and server X.509 PEM certificates and PKCS #8 keys

Separate client and server keystore and truststore files

Configuring node certificates

OpenSearch Security needs to identify requests between the nodes in the cluster. It uses node certificates to secure these requests. The simplest way to configure node certificates is to list the Distinguished Names (DNs) of these certificates in opensearch.yml. All DNs must be included in opensearch.yml on all nodes. Keep in mind that the Security plugin supports wildcards and regular expressions:

plugins.security.nodes_dn:
  - 'CN=node.other.com,OU=SSL,O=Test,L=Test,C=DE'
  - 'CN=*.example.com,OU=SSL,O=Test,L=Test,C=DE'
  - 'CN=elk-devcluster*'
  - '/CN=.*regex/'

If your node certificates have an Object ID (OID) identifier in the SAN section, you can omit this configuration.

Configuring admin certificates

Admin certificates are regular client certificates that have elevated rights to perform administrative tasks. You need an admin certificate to change the Security plugin configuration using plugins/opensearch-security/tools/securityadmin.sh or the REST API. Admin certificates are configured in opensearch.yml by stating their DN(s):

plugins.security.authcz.admin_dn:
  - CN=admin,OU=SSL,O=Test,L=Test,C=DE

For security reasons, you can’t use wildcards or regular expressions here.

(Advanced) OpenSSL

The Security plugin supports OpenSSL, but we only recommend it if you use Java 8. If you use Java 11, we recommend the default configuration.

To use OpenSSL, you must install OpenSSL, the Apache Portable Runtime, and a Netty version with OpenSSL support matching your platform on all nodes.

If OpenSSL is enabled, but for one reason or another the installation does not work, the Security plugin falls back to the Java JCE as the security engine.

(Advanced) Hostname verification and DNS lookup

In addition to verifying the TLS certificates against the root CA and/or intermediate CA(s), the Security plugin can apply additional checks on the transport layer.

With enforce_hostname_verification enabled, the Security plugin verifies that the hostname of the communication partner matches the hostname in the certificate. The hostname is taken from the subject or SAN entries of your certificate. For example, if the hostname of your node is node-0.example.com, then the hostname in the TLS certificate has to be set to node-0.example.com, as well. Otherwise, errors are thrown:

[ERROR][c.a.o.s.s.t.opensearchSecuritySSLNettyTransport] [WX6omJY] SSL Problem No name matching <hostname> found
[ERROR][c.a.o.s.s.t.opensearchSecuritySSLNettyTransport] [WX6omJY] SSL Problem Received fatal alert: certificate_unknown

In addition, when resolve_hostname is enabled, the Security plugin resolves the (verified) hostname against your DNS. If the hostname does not resolve, errors are thrown:

(Advanced) Client authentication

With TLS client authentication enabled, REST clients can send a TLS certificate with the HTTP request to provide identity information to the Security plugin. There are three main usage scenarios for TLS client authentication:

• Providing an admin certificate when using the REST management API.
• Configuring roles and permissions based on a client certificate.
• Providing identity information for tools like OpenSearch Dashboards, Logstash, or Beats.

TLS client authentication has three modes:

• NONE: The Security plugin does not accept TLS client certificates. If one is sent, it is discarded.
• OPTIONAL: The Security plugin accepts TLS client certificates if they are sent, but does not require them.
• REQUIRE: The Security plugin only accepts REST requests when a valid client TLS certificate is sent.

For the REST management API, the client authentication modes has to be OPTIONAL at a minimum.

You can configure the client authentication mode by using the following setting:

(Advanced) Enabled ciphers and protocols

You can limit the allowed ciphers and TLS protocols for the REST layer. For example, you can only allow strong ciphers and limit the TLS versions to the most recent ones.

If this setting is not enabled, the ciphers and TLS versions are negotiated between the browser and the Security plugin automatically, which in some cases can lead to a weaker cipher suite being used. You can configure the ciphers and protocols using the following settings.

Example settings

plugins.security.ssl.http.enabled_ciphers:
  - "TLS_DHE_RSA_WITH_AES_256_CBC_SHA"
  - "TLS_DHE_DSS_WITH_AES_128_CBC_SHA256"
plugins.security.ssl.http.enabled_protocols:
  - "TLSv1.1"
  - "TLSv1.2"

Because it is insecure, the Security plugin disables TLSv1 by default. If you need to use TLSv1 and accept the risks, you can still enable it:

plugins.security.ssl.http.enabled_protocols:
  - "TLSv1"
  - "TLSv1.1"
  - "TLSv1.2"

(Advanced) Disabling client initiated renegotiation for Java 8

Set -Djdk.tls.rejectClientInitiatedRenegotiation=true to disable secure client initiated renegotiation, which is enabled by default. This can be set via OPENSEARCH_JAVA_OPTS in config/jvm.options.

(Advanced) Using encrypted password settings for SSL

The default insecure SSL password settings have been deprecated. In order to use the secure alternative of these settings users can use their alternative forms. Specifically, users can append the _secure suffix to the SSL settings. The resulting secure alternatives are:

• plugins.security.ssl.http.pemkey_password_secure
• plugins.security.ssl.http.keystore_password_secure
• plugins.security.ssl.http.keystore_keypassword_secure
• plugins.security.ssl.http.truststore_password_secure
• plugins.security.ssl.transport.pemkey_password_secure
• plugins.security.ssl.transport.server.pemkey_password_secure
• plugins.security.ssl.transport.client.pemkey_password_secure
• plugins.security.ssl.transport.keystore_password_secure
• plugins.security.ssl.transport.keystore_keypassword_secure
• plugins.security.ssl.transport.server.keystore_keypassword_secure
• plugins.security.ssl.transport.client.keystore_keypassword_secure
• plugins.security.ssl.transport.truststore_password_secure

These settings allow for the use of encrypted passwords in the settings.

Hot reloading TLS certificates

Updating expired or nearly expired TLS certificates does not require restarting the cluster. Instead, enable hot reloading of TLS cerificates by adding the following line to opensearch.yml:

plugins.security.ssl_cert_reload_enabled: true

This setting is false by default.

After enabling hot reloading, use the Reload Certificates API to replace the expired certificates. The API expects the old certificates to be replaced with valid certificates issued with the same Issuer/Subject DN and SAN. The new certificates also need be stored in the same location as the previous certificates in order to prevent any changes to the opensearch.yml file.

Only a superadmin can use the Reload Certificates API.

Reload TLS certificates on the transport layer

The following command reloads TLS certificates on the transport layer:

  curl --cacert <ca.pem> --cert <admin.pem> --key <admin.key> -XPUT https://localhost:9200/_plugins/_security/api/ssl/transport/reloadcerts

You should receive the following response: { "message": "successfully updated transport certs"}

Reload TLS certificates on the http layer

The following command reloads TLS certificates on the http layer:

  curl --cacert <ca.pem> --cert <admin.pem> --key <admin.key> -XPUT https://localhost:9200/_plugins/_security/api/ssl/http/reloadcerts

You should receive the following response:

{ "message": "successfully updated http certs"}