Elasticsearch tuning

This guide summarizes the relevant settings that enable Elasticsearch optimization.

Change users’ password

Changing the default passwords of Elasticsearch is highly recommended in order to improve security.

The following script allows changing the password for a given user. In this example it is used the user admin:

  • Download the script:

    # curl -so wazuh-passwords-tool.sh https://packages.wazuh.com/resources/4.1/open-distro/tools/wazuh-passwords-tool.sh
  • Run the script:

    # bash wazuh-passwords-tool.sh -u admin -p mypassword

This is the output of the script:

Creating backup...
Backup created
Generating hash
Hash generated
Loading changes...
Password changed. Remember to update the password in /etc/filebeat/filebeat.yml and /etc/kibana/kibana.yml if necessary and restart the services.

The script allows changing the password for either a single user or all the users present on the /usr/share/elasticsearch/plugins/opendistro_security/securityconfig/internal_users.yml file. All the available options to run the script are:



-a / –change-all

Generates random passwords, changes all the Open Distro user passwords and prints them on screen

-p / –password <password>

Indicates the new password, must be used with option -u

-u / –user <user>

Indicates the name of the user whose password will be changed. If no password specified it will generate a random one

-v / –verbose

Shows the complete script execution output

-h / –help

Shows help

To generate and change passwords for all users, run the script with the -a option:

  • Run the script:

    # bash wazuh-passwords-tool.sh -a

This is the output of the script:

Generating random passwords
Creating backup...
Backup created
Generating hashes
Hashes generated
Loading changes...

The password for admin is Re6dEMVUcB_c6rEDf_C_nkBCZkwFKtZL

The password for kibanaserver is 4KLxLHor69cq2i1jFXmSUjBTVjG2yhU9

The password for kibanaro is zCd-SrihVwzfRxj5qPrwlSgmZJP9RsMA

The password for logstash is OmbPImuV5fv11R6XYAG92cUjaDy9PkdH

The password for readall is F2vglVGFJHXohwqEW5G4Tfjsiz-qqkTU

The password for snapshotrestore is rd35bCchP3Uf-0w77VCEJzHF7WEP3fNw

Passwords changed. Remember to update the password in /etc/filebeat/filebeat.yml and /etc/kibana/kibana.yml if necessary and restart the services.


The password may need to be updated in both /etc/filebeat/filebeat.yml and /etc/kibana/kibana.yml. After changing the configuration files, remember to restart the corresponding services.

During the installation of Elasticsearch, the passwords for the different users were automatically generated. These passwords can be changed afterwards using API requests. Replace the following variables and execute the corresponding API call:

  • <elasticsearch_ip>: The IP of the Elasticsearch node.

  • <username>: The name of the user whose password is going to be changed.

  • <user_password>: Current user’s password.

  • <new_password>: The new password that will be assigned to the <username> user.

# curl -k -X POST -u <username>:<user_password> "https://<elasticsearch_ip>:9200/_security/user/<username>/_password?pretty" -H 'Content-Type: application/json' -d '
# {
#   "password" : "<new_password>"
# }
# '

If the call was successful it returns an empty JSON structure { }.


The password may need to be updated in /etc/filebeat/filebeat.yml and /etc/kibana/kibana.yml.

Memory locking

Elasticsearch malfunctions when the system is swapping memory. It is crucial for the health of the node that none of the JVM is ever swapped out to disk. The following steps show how to set the bootstrap.memory_lock setting to true so Elasticsearch will lock the process address space into RAM. This prevents any Elasticsearch memory from being swapped out.

  1. Set bootstrap.memory_lock:

    Uncomment or add this line to the /etc/elasticsearch/elasticsearch.yml file:

    bootstrap.memory_lock: true
  2. Edit the limit of system resources:

    Where to configure system settings depends on which package and operating system used for the Elasticsearch installation.

    In a case where systemd is used, system limits need to be specified via systemd. To do this, create the folder executing the command:

    # mkdir -p /etc/systemd/system/elasticsearch.service.d/

    Then, in the new directory, add a file called elasticsearch.conf and specify any changes in that file:

    # cat > /etc/systemd/system/elasticsearch.service.d/elasticsearch.conf << EOF

    Edit the proper file /etc/sysconfig/elasticsearch for RPM or /etc/default/elasticsearch for Debian:

  3. Limit memory:

    The previous configuration might cause node instability or even node death with an OutOfMemory exception if Elasticsearch tries to allocate more memory than is available. JVM heap limits will help limit memory usage and prevent this situation. Two rules must be applied when setting Elasticsearch’s heap size:

    • Use no more than 50% of available RAM.

    • Use no more than 32 GB.

    It is also important to consider the memory usage of the operating system, services and software running on the host. By default, Elasticsearch is configured with a heap of 1 GB. It can be changed via JVM flags using the /etc/elasticsearch/jvm.options file:

    # Xms represents the initial size of total heap space
    # Xmx represents the maximum size of total heap space


    The values min (Xms) and max (Xmx) sizes must be the same to prevent JVM heap resizing at runtime as this is a very costly process.

  4. Restart Elasticsearch:

# systemctl daemon-reload
# systemctl restart elasticsearch
# service elasticsearch restart

After starting Elasticsearch, run the following request to verify that the setting was successfully changed by checking the value of mlockall:

# curl "http://localhost:9200/_nodes?filter_path=**.mlockall&pretty"
  "nodes" : {
    "sRuGbIQRRfC54wzwIHjJWQ" : {
      "process" : {
        "mlockall" : true

If the output of the "mlockall" field is false, the request has failed. In addition, the following line will appear in /var/log/elasticsearch/elasticsearch.log:

Unable to lock JVM Memory


Shards and replicas

Elasticsearch offers the possibility to split an index into multiple segments called shards. Each shard is in itself a fully functional and independent “index” that can be hosted on any node in the cluster. The splitting is important for two main reasons:

  • Horizontal scalation.

  • Distribute and parallelize operations across shards, increasing the performance and throughput.

In addition, Elasticsearch allows the user to make one or more copies of the index shards in what are called replica shards, or replicas for short. Replication is important for two main reasons

  • It provides high availability in case a shard or node fails.

  • It allows search volume and throughput to scale, since searches can be executed on all replicas in parallel.


The number of shards and replicas can be defined per index at the time of their creation. Once the index is created, the number of replicas must be changed dynamically, whereas the number of fragments cannot be changed afterwards.

How many shards should an index have?

As it is not possible to reshard (changing the number of shards) without reindexing, careful consideration should be given to how many shards will be needed before creating the first index. The number of nodes in the installation will influence the number of shards to be planned. In general, the most optimal performance will be realized by using the same number of shards as nodes. Thus, a cluster with three nodes should have three shards, while a cluster with one node would only need one shard.

How many replicas should an index have?

Here is an example of how a cluster with three nodes and three shards could be set up:

  • No replica: Each node has one shard. If a node goes down, an incomplete index of two fragments will remain.

  • One replica: Each node has one shard and one replica. If a node goes down, a full index will remain.

  • Two replicas: Each node has one shard and two replicas (the full index). With this setup, the cluster can continue to operate even if two nodes go down. Although this seems to be the best solution, it increases the storage requirements.

Setting the number of shards and replicas

The default installation of Elasticsearch will configure each index with 3 primary shards and no replicas.

To change these settings, the Elasticsearch’s template will have to be edited. In the following example, the proper values for shards and replicas are configured in a cluster with only one node.


If the index has already been created, it must be reindexed after editing the template.

  1. Download the Wazuh Elasticsearch template:

    # curl https://raw.githubusercontent.com/wazuh/wazuh/v4.1.5/extensions/elasticsearch/7.x/wazuh-template.json -o w-elastic-template.json
  2. Edit the template w-elastic-template.json in order to set one shard with no replicas:

      "order": 1,
      "index_patterns": ["wazuh-alerts-4.x-*"],
      "settings": {
        "index.refresh_interval": "5s",
        "index.number_of_shards": "3",
        "index.number_of_replicas": "0",
        "index.auto_expand_replicas": "0-1",
        "index.mapping.total_fields.limit": 2000
      "mappings": {
      "...": "..."


    The value “order” is set to “1”, otherwise Filebeat will overwrite the existing template. Multiple matching templates with the same order value will result in a non-deterministic merging order.

  3. Load the template:

    # curl -X PUT "http://localhost:9200/_template/wazuh-custom" -H 'Content-Type: application/json' -d @w-elastic-template.json
    { "acknowledged" : true }
  4. Optional. Confirm that the configuration was successfully updated:

    # curl "https://localhost:9200/_template/wazuh-custom?pretty&filter_path=wazuh-custom.settings" -k -u admin:admin

    In case of having changed the admin’s user credentials, the admin:admin must be modified in consequence.

      "wazuh-custom" : {
        "settings" : {
          "index" : {
            "mapping" : {
              "total_fields" : {
                "limit" : "2000"
            "refresh_interval" : "5s",
            "number_of_shards" : "3",
            "auto_expand_replicas" : "0-1",
            "number_of_replicas" : "1"

Changing the number of replicas

The number of replicas can be changed dynamically using the Elasticsearch API. In a cluster with one node, the number of replicas should be set to zero:

# curl -X PUT "http://localhost:9200/wazuh-alerts-\*/_settings?pretty" -H 'Content-Type: application/json' -d'
  "settings" : {
    "number_of_replicas" : 0

More information about configuring shards and replicas can be found in the Kibana configuration section.