[[node-certificates]]
==== Generating Node Certificates

TLS requires X.509 certificates to perform encryption and authentication of the
application that is being communicated with. In order for the communication
between nodes to be truly secure, the certificates must be validated. The
recommended approach for validating certificate authenticity in an {es} cluster
is to trust the certificate authority (CA) that signed the certificate. By doing
this, as nodes are added to your cluster they just need to use a certificate
signed by the same CA and the node is automatically allowed to join the cluster.
Additionally, it is recommended that the certificates contain subject alternative
names (SAN) that correspond to the node's IP address and DNS name so that
hostname verification can be performed.

The {ref}/certutil.html[`elasticsearch-certutil`] command simplifies the process
of generating certificates for the {stack}. It takes care of generating a CA and
signing certificates with the CA. It can be used interactively or in a silent
mode through the use of an input file. It also supports generation of
certificate signing requests (CSR), so that a commercial- or
organization-specific CA can be used to sign the certificates. For example:

. Optional: Create a certificate authority for your {es} cluster.
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For example, use the `elasticsearch-certutil ca` command:

[source,shell]
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bin/elasticsearch-certutil ca
----------------------------------------------------------

You can configure the cluster to trust all nodes that have a certificate that
has been signed by this CA.

The command outputs a single file, with a default name of `elastic-stack-ca.p12`.
This file is a PKCS#12 keystore that contains the public certificate for your CA
and the private key that is used to sign the certificates for each node.

The `elasticsearch-certutil` command also prompts you for a password to protect
the file and key. If you plan to add more nodes to your cluster in the future,
retain a copy of the file and remember its password.
--

. Generate a certificate and private key for each node in your cluster.
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--
For example, use the `elasticsearch-certutil cert` command:

[source,shell]
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bin/elasticsearch-certutil cert --ca elastic-stack-ca.p12
----------------------------------------------------------
The output is a single PKCS#12 keystore that includes the node certificate, node
key, and CA certificate.

You are also prompted for a password. You can enter a password for your
certificate and key, or you can leave the password blank by pressing Enter.

By default `elasticsearch-certutil` generates certificates that have no hostname
information in them (that is, they do not have any Subject Alternative Name
fields). This means that you can use the certificate for every node in your
cluster, but you must turn off hostname verification as shown in the
configuration below.

If you want to use hostname verification within your cluster, run the
`elasticsearch-certutil cert` command once for each of your nodes and provide
the `--name`, `--dns` and `--ip` options.

NOTE: You should secure the output files, since they contain the private keys
for your instance.

Alternatively, if you want to use a commercial or organization-specific CA,
you can use the `elasticsearch-certutil csr` command to generate certificate
signing requests (CSR) for the nodes in your cluster. For more information, see
<<certutil>>.
--

. Copy the node certificate to the appropriate locations.
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--
Copy the applicable `.p12` file into a directory within the {es} configuration
directory on each node. For example, `/home/es/config/certs`. There is no need
to copy the CA file to this directory.

For each additional Elastic product that you want to configure, copy the
certificates to the relevant configuration directory. 
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NOTE: If you choose not to use `elasticsearch-certutil`, the certificates that
you obtain must allow for both `clientAuth` and `serverAuth` if the extended key
usage extension is present. The certificates need to be in PEM or PKCS#12
format. Although not required, it is highly recommended that the certificate
contain the DNS names and/or IP addresses of the node so that hostname
verification can be used.