Generate Wildcard SSL Certificates for Elasticsearch

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Generate Wildcard SSL Certificates for Elasticsearch

Is there an easy way to generate wildcard SSL certificates for Elasticsearch? Yes, definitely. The current Elasticsearch releases, Elasticsearch 8.x, when installed, the HTTP and Transport layers are configured with SSL/TLS certificates automatically by default. The challenge with this however, especially for the HTTP layer, is that a certificate, whose common name is tied to the node’s hostname and localhost, is generated. If you wanted to use this certificate in the cluster, it will be a bit challenging. Wildcard SSL certificates offer a convenient and effective approach to secure Elasticsearch deployments, enabling seamless encryption across multiple domains or subdomains under a single certificate.

Generate Wildcard SSL Certificates for Elasticsearch

So, how can you generate Wildcard SSL certificates for Elasticsearch? Remember, we are only talking about SSL/TLS certificates for the HTTP layer.

Elasticsearch nodes in a cluster communicate with each other through the transport layer via transport protocol on port 9300/tcp while REST clients such as Beats, Kibana, Logstash or any other client, communicate with Elasticsearch through the HTTP layer via the HTTP protocol on port 9200/tcp.

Install and Setup Elasticsearch

We assume that you have a running cluster. If not, you can check our guides on how to install and setup ELK stack;

Install and Setup ELK Stack

Generate Elasticsearch Certificate Authority

So, you can use existing CA files generated automatically during install or create your own.

Use Existing CA Files

When Elasticsearch 8.x is installed, it automatically enables and configures SSL/TLS on both the HTTP and Transport layer. In the process, it generates CA and associated certificate files.

The certificate files are stored in the /etc/elasticsearch/certs/ directory.

ls -1 /etc/elasticsearch/certs/
http_ca.crt
http.p12
transport.p12
  • http_ca.crt: This file contains the CA certificate for the Elasticsearch cluster. The CA certificate is used to verify the authenticity of the server certificates that are used by Elasticsearch nodes.
  • http.p12: The PKCS#12 file contains the server certificate and private key for the HTTP REST interface as well as the CA key.
  • transport.p12: The PKCS#12 file contains the client certificate and private key for the Transport client interface.

Similarly, you can confirm the Elasticsearch configuration;

less /etc/elasticsearch/elasticsearch.yml
...xpack.security.enabled: true
xpack.security.enrollment.enabled: true
xpack.security.http.ssl:
  enabled: true
  keystore.path: certs/http.p12
xpack.security.transport.ssl:
  enabled: true
  verification_mode: certificate
  keystore.path: certs/transport.p12
  truststore.path: certs/transport.p12
...

Create Own Elasticsearch Certificate Authority

You can also create your own Elasticsearch CA. Hence, create a directory to store the certificates if you don’t have one already.

[[ -d /etc/elasticsearch/es-certs ]] || mkdir /etc/elasticsearch/es-certs

Generate the Certificate Authority (CA). By default, the CA is generated in PKCS#12 format. To generate them in the usual PEM format, pass --pem option.

/usr/share/elasticsearch/bin/elasticsearch-certutil ca \
	--pem \
	--days 3650 \
	--out /etc/elasticsearch/es-certs/elkstack-ca.zip

You can as well run the command as below and go through the prompts to generate the CA.

/usr/share/elasticsearch/bin/elasticsearch-certutil ca

The output zip file will contain individual files for the CA certificate and private key

unzip -l /etc/elasticsearch/es-certs/elkstack-ca.zip
Archive:  /etc/elasticsearch/es-certs/elkstack-ca.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  2023-11-24 16:38   ca/
     1200  2023-11-24 16:38   ca/ca.crt
     1675  2023-11-24 16:38   ca/ca.key
---------                     -------
     2875                     3 files

Unzip the file to get the CA required to generate the TLS certs.

unzip -d /etc/elasticsearch/es-certs /etc/elasticsearch/es-certs/elkstack-ca.zip
Archive:  /etc/elasticsearch/es-certs/elkstack-ca.zip
   creating: /etc/elasticsearch/es-certs/ca/
  inflating: /etc/elasticsearch/es-certs/ca/ca.crt  
  inflating: /etc/elasticsearch/es-certs/ca/ca.key 

You should now have the ca/ca.crt and ca/ca.key in PEM format in the certs directory as shown above.

Generate Wildcard SSL Certificates for Elasticsearch

Now that you have the CA certificates, you can generate and sign your HTTP certificates for the Elasticseach cluster.

Using Existing CA to Generate Wildcard Certificates

If you want to use the CA certificates generated automatically during the installation of Elasticsearch to generate wildcard SSL/TLS certificates for Elasticsearch HTTP interface, then proceed as follows.

The /etc/elasticsearch/certs/http.p12 file contains the server certificate and private key for the HTTP REST interface as well as the CA key.

However, this certificate will have its common name tied to the FQDN of the Elasticsearch node. This means that, if you have a cluster of nodes, it becomes a challenge on how to define Elasticsearch host name on the clients side if you want to sent logs to other nodes in the cluster.

Example error when you try to connect to ES using Filebeat with the ES host not matching the exact ES node;

"message":"Failed to connect to backoff(elasticsearch(https://elk.kifarunix-demo.com:9200)): Get \"https://elk.kifarunix-demo.com:9200\": x509: certificate is valid for localhost, es-node01.kifarunix-demo.com, not elk.kifarunix-demo.com"

To generate wildcard SSL certificates from the existing CA, then you need to have the CA key.

To get the CA key, you first need to retrieve the password that was used to protect it by executing the command below;

/usr/share/elasticsearch/bin/elasticsearch-keystore show xpack.security.http.ssl.keystore.secure_password

The command will print the Keystore password to standard output.

Once you have the Keystore password, extract the CA key;

openssl pkcs12 -in /etc/elasticsearch/certs/http.p12 -nodes

You will be prompted to enter the keystore password. Use the one retrieved above.

The command will print keys each with a friendlyName, e.g, friendlyName: http_ca and friendlyName: http.

MAC: sha256, Iteration 10000
MAC length: 32, salt length: 20
PKCS7 Data
Shrouded Keybag: PBES2, PBKDF2, AES-256-CBC, Iteration 10000, PRF hmacWithSHA256
Bag Attributes
    friendlyName: http_ca
    localKeyID: 54 69 6D 65 20 31 37 30 30 37 35 38 35 31 39 32 33 39 
Key Attributes: 
-----BEGIN PRIVATE KEY-----
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-----END PRIVATE KEY-----
Shrouded Keybag: PBES2, PBKDF2, AES-256-CBC, Iteration 10000, PRF hmacWithSHA256
Bag Attributes
    friendlyName: http
    localKeyID: 54 69 6D 65 20 31 37 30 30 37 35 38 35 31 39 32 36 32 
Key Attributes: 
-----BEGIN PRIVATE KEY-----
MIIJQwIBADANBgkqhkiG9w0BAQEFAASCCS0wggkpAgEAAoICAQC8kJYcWvgzcjRd
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-----END PRIVATE KEY-----
PKCS7 Encrypted data: PBES2, PBKDF2, AES-256-CBC, Iteration 10000, PRF hmacWithSHA256
Certificate bag
Bag Attributes
    friendlyName: http_ca
    localKeyID: 54 69 6D 65 20 31 37 30 30 37 35 38 35 31 39 32 33 39 
subject=CN = Elasticsearch security auto-configuration HTTP CA
issuer=CN = Elasticsearch security auto-configuration HTTP CA
-----BEGIN CERTIFICATE-----
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-----END CERTIFICATE-----
Certificate bag
Bag Attributes
    friendlyName: http
    localKeyID: 54 69 6D 65 20 31 37 30 30 37 35 38 35 31 39 32 36 32 
subject=CN = es-node01.kifarunix-demo.com
issuer=CN = Elasticsearch security auto-configuration HTTP CA
-----BEGIN CERTIFICATE-----
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-----END CERTIFICATE-----
Certificate bag
Bag Attributes
    friendlyName: CN=Elasticsearch security auto-configuration HTTP CA
subject=CN = Elasticsearch security auto-configuration HTTP CA
issuer=CN = Elasticsearch security auto-configuration HTTP CA
-----BEGIN CERTIFICATE-----
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m8+PkmhYNPJDUcVa2p7EBBYN1GbYOCZJi6VfCaMYfWb7i/HwjNY5TAkxH/aujsy6
hXHQVkpmiGrUPbSDilcGLbKyCzhSAqvmrA7wSQOGgtlnDaSygNf2HK5nI2ieaHpB
eD6RLuQG2KsRkwaZqCBAHmT2MJgygFnPWz+AJ3CTPJdeEoP9Bm9iJtksdDLk7nRz
1JTCcSXXSYpa43Xaxt8UaBocuU8KKZbwiKWy7b/LyBML5fWY91QXDeet7iVhtb5U
ACF5KnFSKyPDtqZ6bRfdPJkNltjsefipnWUl5RC7
-----END CERTIFICATE-----

The CA key will be the one under the friendlyName: http_ca. By the way, you can also confirm the common name of the certificate from the output above.

You can copy the CA key (under the friendlyName: http_ca), anything between -----BEGIN PRIVATE KEY----- and -----END PRIVATE KEY----- and store it in a file of your choice, e.g /etc/elasticsearch/certs/http_ca_key.crt.

Once you have the CA key, execute the command below to generate wildcard certificates. Answer the prompts accordingly.

/usr/share/elasticsearch/bin/elasticsearch-certutil http
  • Generate a CSR, enter n.
  • Use an existing CA, enter y.
  • Enter the absolute path to your new CA certificate, such as the path to the /etc/elasticsearch/certs/http_ca.crt file.
  • Enter the absolute path to your new CA certificate private key, such as the path to the ca.key file.
  • Enter an expiration value for your certificate. You can enter the validity period in years, months, or days. For example, enter 5y for one year.
  • When asked if you want to generate one certificate per node, enter n. Here, we need Wildcard SSL/TLS certs.
  • When prompted, enter the hostnames, enter all hostnames used to connect to your first node. These hostnames will be added as DNS names in the Subject Alternative Name (SAN) field in your certificate. List every hostname and variant used to connect to your cluster over HTTPS. For the the wildcard certificates, then use a wildcard of your domain, e.g, *.kifarunix-demo.com. Press ENTER double and confirm the changes
  • Enter the IP addresses that clients can use to connect to your node. Just press Enter to leave blank.
  • Confirm if you need to make any changes, if not proceed.
  • Set keystore password to protect the keys.
  • Enter the filename into which to save lives.

You should now see the certificate files archived in the filename you provided.

unzip -l /usr/share/elasticsearch/elasticsearch-ssl-http.zip
Archive:  /usr/share/elasticsearch/elasticsearch-ssl-http.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  2023-11-24 15:03   elasticsearch/
     1365  2023-11-24 15:03   elasticsearch/README.txt
     4452  2023-11-24 15:03   elasticsearch/http.p12
      850  2023-11-24 15:03   elasticsearch/sample-elasticsearch.yml
        0  2023-11-24 15:03   kibana/
     1306  2023-11-24 15:03   kibana/README.txt
     1915  2023-11-24 15:03   kibana/elasticsearch-ca.pem
     1057  2023-11-24 15:03   kibana/sample-kibana.yml
---------                     -------
    10945                     8 files

The wildcard CA file for our domain is the one under Kibana directory in the archive above. You can use that with all clients sending data to Elasticsearch.

The http.p12 will contain the server’s certificate and keys.

You can extract to your preferred location. You will have two directories, elasticsearch and kibana, each containing the cert/CA files and a README.txt explaining how to use these files.

mkdir /etc/elasticsearch/certs
unzip -d /etc/elasticsearch/certs/ /usr/share/elasticsearch/elasticsearch-ssl-http.zip
chown -R :elasticsearch /etc/elasticsearch/certs/

Configure Elasticsearch, in the cluster to use new wildcard certificates;

vim /etc/elasticsearch/elasticsearch.yml
...
# Enable encryption for HTTP API client connections, such as Kibana, Logstash, and Agents
xpack.security.http.ssl:
  enabled: true
#  keystore.path: certs/http.p12
  keystore.path: certs/elasticsearch/http.p12
...

Save and exit the file.

Restart Elasticsearch.

systemctl restart elasticsearch

Similarly, configure Filebeat, Logstash, Kibana or any other client connecting to Elasticsearch to use the new CA certificate.

You can download the certificate directly on the client from the Elasticsearch using openssl command;

openssl s_client -connect elk.kifarunix-demo.com:9200 -showcerts | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p'

The save whatever between the -----BEGIN CERTIFICATE----- and -----END CERTIFICATE----- in a file as ES CA certificate file.

You can run certificate verification against the server. For example;

openssl s_client -connect elk.kifarunix-demo.com:9200 -CAfile /etc/filebeat/es-ca.crt

You should get verification is okay.

subject=DC = com, CN = kifarunix-demo

issuer=CN = Elasticsearch security auto-configuration HTTP CA

---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 3065 bytes and written 400 bytes
Verification: OK
---
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)

Using Newly Created CA to Generate Wildcard Certificates

Our newly generated CA certificate and the key are stored under /etc/elasticsearch/es-certs/ca/.

To generate the wildcard SSL/TLS Elasticsearch certificates, you can use the /usr/share/elasticsearch/bin/elasticsearch-certutil cert.

/usr/share/elasticsearch/bin/elasticsearch-certutil cert \
	--name elkstack-certs \
	--ca-cert /etc/elasticsearch/es-certs/ca/ca.crt \
	--ca-key /etc/elasticsearch/es-certs/ca/ca.key \
	--pem \
	--dns '*.kifarunix-demo.com' \
	--days 3650 \
	--out /etc/elasticsearch/es-certs/elkstack-certs.zip

If you generated CA in PKCS12 format, then you will need to extract the CA key to allow you create the certificates using the CA.

Once you have the certificates, you can install them accordingly.

Note that if you set the password for your private key while generating the certificates, then you need to add the password to the keystore to the secure settings in Elasticsearch.

/usr/share/elasticsearch/bin/elasticsearch-keystore add xpack.security.http.ssl.keystore.secure_password

Ensure the keystore password is same across the cluster!

Similarly, configure your Elasticsearch to use the new CA. If you are using certificates in PEM format, then your Elasticsearch configuration will look like;

xpack.security.http.ssl:
  enabled: true
  key: /etc/elasticsearch/certs/es-certs/elkstack-certs.key
  certificate: /etc/elasticsearch/certs/es-certs/elkstack-certs.crt
  certificate_authorities: /etc/elasticsearch/certs/ca/ca.crt

Configure the clients to use the certificate accordingly.

Using Commercial CA Signed Certificates

If you have wildcards certs from a commercial CA, then by all means, configure Elasticsreach as well as ES clients to use them.

That brings us to a close of our guide on how to generate wildcard SSL certificates for Elasticsearch.

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Kifarunix
Linux Certified Engineer, with a passion for open-source technology and a strong understanding of Linux systems. With experience in system administration, troubleshooting, and automation, I am skilled in maintaining and optimizing Linux infrastructure.

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