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Securing Communication With Logstash by Using SSL

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Securing Communication With Logstash by Using SSL

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You can use SSL mutual authentication to secure connections between Filebeat and Logstash. This ensures that Filebeat sends encrypted data to trusted Logstash servers only, and that the Logstash server receives data from trusted Filebeat clients only.

To use SSL mutual authentication:

Create a certificate authority (CA) and use it to sign the certificates that you plan to use for Filebeat and Logstash. Creating a correct SSL/TLS infrastructure is outside the scope of this document. There are many online resources available that describe how to create certificates.
Configure Filebeat to use SSL. In the filebeat.yml config file, specify the following settings under ssl:
- certificate_authorities: Configures Filebeat to trust any certificates signed by the specified CA. If certificate_authorities is empty or not set, the trusted certificate authorities of the host system are used.
- certificate and key: Specifies the certificate and key that Filebeat uses to authenticate with Logstash.
  
  For example:
```
output.logstash:
  hosts: ["logs.mycompany.com:5044"]
  ssl.certificate_authorities: ["/etc/ca.crt"]
  ssl.certificate: "/etc/client.crt"
  ssl.key: "/etc/client.key"
```
  For more information about these configuration options, see SSL Configuration.
Configure Logstash to use SSL. In the Logstash config file, specify the following settings for the Beats input plugin for Logstash:
- ssl: When set to true, enables Logstash to use SSL/TLS.
- ssl_certificate_authorities: Configures Logstash to trust any certificates signed by the specified CA.
- ssl_certificate and ssl_key: Specify the certificate and key that Logstash uses to authenticate with the client.
- ssl_verify_mode: Specifies whether the Logstash server verifies the client certificate against the CA. You need to specify either peer or force_peer to make the server ask for the certificate and validate it. If you specify force_peer, and Filebeat doesn’t provide a certificate, the Logstash connection will be closed.
  
  For example:
```
input {
  beats {
    port => 5044
    ssl => true
    ssl_certificate_authorities => ["/etc/ca.crt"]
    ssl_certificate => "/etc/server.crt"
    ssl_key => "/etc/server.key"
    ssl_verify_mode => "force_peer"
  }
}
```
  For more information about these options, see the documentation for the Beats input plugin.

Validating the Logstash Server’s Certificate

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Before running Filebeat, you should validate the Logstash server’s certificate. You can use curl to validate the certificate even though the protocol used to communicate with Logstash is not based on HTTP. For example:

curl -v --cacert ca.crt https://logs.mycompany.com:5044

If the test is successful, you’ll receive an empty response error:

* Rebuilt URL to: https://logs.mycompany.com:5044/
*   Trying 192.168.99.100...
* Connected to logs.mycompany.com (192.168.99.100) port 5044 (#0)
* TLS 1.2 connection using TLS_DHE_RSA_WITH_AES_256_CBC_SHA
* Server certificate: logs.mycompany.com
* Server certificate: mycompany.com
> GET / HTTP/1.1
> Host: logs.mycompany.com:5044
> User-Agent: curl/7.43.0
> Accept: */*
>
* Empty reply from server
* Connection #0 to host logs.mycompany.com left intact
curl: (52) Empty reply from server

The following example uses the IP address rather than the hostname to validate the certificate:

curl -v --cacert ca.crt https://192.168.99.100:5044

Validation for this test fails because the certificate is not valid for the specified IP address. It’s only valid for the logs.mycompany.com, the hostname that appears in the Subject field of the certificate.

* Rebuilt URL to: https://192.168.99.100:5044/
*   Trying 192.168.99.100...
* Connected to 192.168.99.100 (192.168.99.100) port 5044 (#0)
* WARNING: using IP address, SNI is being disabled by the OS.
* SSL: certificate verification failed (result: 5)
* Closing connection 0
curl: (51) SSL: certificate verification failed (result: 5)

See the troubleshooting docs for info about resolving this issue.

Testing the Beats to Logstash Connection

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If you have Filebeat running as a service, first stop the service. Then test your setup by running Filebeat in the foreground so you can quickly see any errors that occur:

filebeat -c filebeat.yml -e -v

Any errors will be printed to the console. See the troubleshooting docs for info about resolving common errors.

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