SSL Client Connections

The Java truststore enables Horizon to establish SSL connections with monitored nodes.

Horizon uses the system truststore that is associated with your Java installation. It should contain all of the certificates that Horizon needs to verify trust when making connections during polling or collection.

Because any changes to the system truststore may be overwritten if you upgrade or reinstall Java, you can instead specify a custom truststore for Horizon to use.

Import certificate to Java truststore

Use the following console commands to import a certificate to your Java truststore:

keytool \
  -import \ (1)
  -v \ (2)
  -trustcacerts \ (3)
  -alias localhost \ (4)
  -file localhost.cert \ (5)
  -keystore ${OPENNMS_HOME}/etc/trust-store.jks (6)
1 Define a certificate or a certificate chain import.
2 Use verbose output.
3 Trust certificates from cacerts.
4 The alias for the certificate to import (for example, the common name).
5 The certificate to import.
6 The location of the Java truststore. If this file does not exist, it will be created.

If you create a new Java truststore, you must set its password. If you update an existing Java truststore, type the password that you chose when you first created the truststore.

(Optional) Download existing public certificate

Use the following command to download an existing public certificate:

openssl \
  s_client \ (1)
  -showcerts \ (2)
  -connect localhost:443 \ (3)
  -servername localhost \ (4)
  < /dev/null \ (5)
  > localhost.cert (6)
1 Use SSL/TLS client functionality of openssl.
2 Show all certificates in the chain.
3 PORT:HOST to connect to (for example, localhost:443).
4 Optional. If you are serving multiple certificates under one IP address, you may define a server name; otherwise, the ip of localhost:PORT certificate is returned, which may not match the requested server name (,,
5 No input.
6 Where to store the certificate.

Configure Horizon to use the Java truststore

You must configure the appropriate* properties to set Horizon to use your desired Java truststore. To do so, edit or create ${OPENNMS_HOME}/etc/ and add the following properties:${OPENNMS_HOME}/etc/trust-store.jks

For more details on the Java built-in SSL system properties, see Debugging/Properties.

Each time you modify the Java truststore, you must restart Horizon services for the changes to take effect.

Differences between Java truststore and keystore

The Java truststore determines whether a remote connection should be trusted—​in other words, whether a remote party is who it claims to be. It serves as a client use case.

The Java keystore decides which authentication credentials should be sent to the remote host for authentication during an SSL handshake. It serves as a server use case.

For more information, see the JSSE Reference Guide.


If you encounter issues while using SSL, it might be useful to enable debug logging. You could also use one of the built-in Java system properties to configure SSL:

System Property Name Description

Location of the keystore file that contains the application process’s certificate and private key.

Password to access the private key from the keystore file specified by This password is used twice: once to unlock the keystore file (store password), and once to decrypt the private key stored in the keystore (key password). The JSSE framework requires these passwords to be identical.

(Optional) Keystore type. Defaults to jks.

Location of the truststore file that contains the CA certificates that the application process trusts. If this property does not specify a truststore location, the Java implementation searches for and uses a keystore file from the following locations, in order:
* ${JAVA_HOME}/lib/security/jssecacerts * ${JAVA_HOME}/lib/security/cacerts

Password to unlock the truststore file.

(Optional) Truststore type. Defaults to jks.

(Optional) Controls logging for the SSL/TLS layer. To enable, set this property to ssl.
For more details about possible values, see debugging utilities in the official Oracle documentation.