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Configuration Files

The ClickHouse server can be configured with configuration files in XML or YAML syntax. In most installation types, the ClickHouse server runs with /etc/clickhouse-server/config.xml as default configuration file but it is also possible to specify the location of the configuration file manually at server startup using command line option --config-file= or -C. Additional configuration files may be placed into directory config.d/ relative to the main configuration file, for example into directory /etc/clickhouse-server/config.d/. Files in this directory and the main configuration are merged in a preprocessing step before the configuration is applied in ClickHouse server. Configuration files are merged in alphabetical order. To simplify updates and improve modularization, it is best practice to keep the default config.xml file unmodified and place additional customization into config.d/.

It is possible to mix XML and YAML configuration files, for example you could have a main configuration file config.xml and additional configuration files config.d/network.xml, config.d/timezone.yaml and config.d/keeper.yaml. Mixing XML and YAML within a single configuration file is not supported. XML configuration files should use <clickhouse>...</clickhouse> as top-level tag. In YAML configuration files, clickhouse: is optional, the parser inserts it implicitly if absent.

Overriding Configuration​

The merge of configuration files behaves as one intuitively expects: The contents of both files are combined recursively, children with the same name are replaced by the element of the more specific configuration file. The merge can be customized using attributes replace and remove.

  • Attribute replace means that the element is replaced by the specified one.
  • Attribute remove means that the element is deleted.

To specify that a value of an element should be replaced by the value of an environment variable, you can use attribute from_env.

Example with $MAX_QUERY_SIZE = 150000:

<clickhouse>
    <profiles>
        <default>
            <max_query_size from_env="MAX_QUERY_SIZE"/>
        </default>
    </profiles>
</clickhouse>

which is equal to

<clickhouse>
    <profiles>
        <default>
            <max_query_size/>150000</max_query_size>
        </default>
    </profiles>
</clickhouse>

Substituting Configuration​

The config can also define “substitutions”. If an element has the incl attribute, the corresponding substitution from the file will be used as the value. By default, the path to the file with substitutions is /etc/metrika.xml. This can be changed in the include_from element in the server config. The substitution values are specified in /clickhouse/substitution_name elements in this file. If a substitution specified in incl does not exist, it is recorded in the log. To prevent ClickHouse from logging missing substitutions, specify the optional="true" attribute (for example, settings for macros).

If you want to replace an entire element with a substitution use include as the element name.

XML substitution example:

<clickhouse>
    <!-- Appends XML subtree found at `/profiles-in-zookeeper` ZK path to `<profiles>` element. -->
    <profiles from_zk="/profiles-in-zookeeper" />

    <users>
        <!-- Replaces `include` element with the subtree found at `/users-in-zookeeper` ZK path. -->
        <include from_zk="/users-in-zookeeper" />
        <include from_zk="/other-users-in-zookeeper" />
    </users>
</clickhouse>

Substitutions can also be performed from ZooKeeper. To do this, specify the attribute from_zk = "/path/to/node". The element value is replaced with the contents of the node at /path/to/node in ZooKeeper. You can also put an entire XML subtree on the ZooKeeper node and it will be fully inserted into the source element.

Encrypting and Hiding Configuration​

You can use symmetric encryption to encrypt a configuration element, for example, a plaintext password or private key. To do so, first configure the encryption codec, then add attribute encrypted_by with the name of the encryption codec as value to the element to encrypt.

Unlike attributes from_zk, from_env and incl (or element include), no substitution, i.e. decryption of the encrypted value, is performed in the preprocessed file. Decryption happens only at runtime in the server process.

Example:

<clickhouse>

    <encryption_codecs>
        <aes_128_gcm_siv>
            <key_hex>00112233445566778899aabbccddeeff</key_hex>
        </aes_128_gcm_siv>
    </encryption_codecs>

    <interserver_http_credentials>
        <user>admin</user>
        <password encrypted_by="AES_128_GCM_SIV">961F000000040000000000EEDDEF4F453CFE6457C4234BD7C09258BD651D85</password>
    </interserver_http_credentials>

</clickhouse>

To encrypt a value, you can use the (example) program encrypt_decrypt:

Example:

./encrypt_decrypt /etc/clickhouse-server/config.xml -e AES_128_GCM_SIV abcd
961F000000040000000000EEDDEF4F453CFE6457C4234BD7C09258BD651D85

Even with encrypted configuration elements, encrypted elements still appear in the preprocessed configuration file. If this is a problem for your ClickHouse deployment, we suggest two alternatives: either set file permissions of the preprocessed file to 600 or use the hide_in_preprocessed attribute.

Example:

<clickhouse>

    <interserver_http_credentials hide_in_preprocessed="true">
        <user>admin</user>
        <password>secret</password>
    </interserver_http_credentials>

</clickhouse>

User Settings​

The config.xml file can specify a separate config with user settings, profiles, and quotas. The relative path to this config is set in the users_config element. By default, it is users.xml. If users_config is omitted, the user settings, profiles, and quotas are specified directly in config.xml.

Users configuration can be split into separate files similar to config.xml and config.d/. Directory name is defined as users_config setting without .xml postfix concatenated with .d. Directory users.d is used by default, as users_config defaults to users.xml.

Note that configuration files are first merged taking into account Override settings and includes are processed after that.

XML example​

For example, you can have separate config file for each user like this:

$ cat /etc/clickhouse-server/users.d/alice.xml
<clickhouse>
    <users>
      <alice>
          <profile>analytics</profile>
            <networks>
                  <ip>::/0</ip>
            </networks>
          <password_sha256_hex>...</password_sha256_hex>
          <quota>analytics</quota>
      </alice>
    </users>
</clickhouse>

YAML examples​

Here you can see default config written in YAML: config.yaml.example.

There are some differences between YAML and XML formats in terms of ClickHouse configurations. Here are some tips for writing a configuration in YAML format.

An XML tag with a text value is represented by a YAML key-value pair

key: value

Corresponding XML:

<key>value</value>

A nested XML node is represented by a YAML map:

map_key:
  key1: val1
  key2: val2
  key3: val3

Corresponding XML:

<map_key>
    <key1>val1</key1>
    <key2>val2</key2>
    <key3>val3</key3>
</map_key>

To create the same XML tag multiple times, use a YAML sequence:

seq_key:
  - val1
  - val2
  - key1: val3
  - map:
      key2: val4
      key3: val5

Corresponding XML:

<seq_key>val1</seq_key>
<seq_key>val2</seq_key>
<seq_key>
    <key1>val3</key1>
</seq_key>
<seq_key>
    <map>
        <key2>val4</key2>
        <key3>val5</key3>
    </map>
</seq_key>

To provide an XML attribute, you can use an attribute key with a @ prefix. Note that @ is reserved by YAML standard, so must be wrapped in double quotes:

map:
  "@attr1": value1
  "@attr2": value2
  key: 123

Corresponding XML:

<map attr1="value1" attr2="value2">
    <key>123</key>
</map>

It is also possible to use attributes in YAML sequence:

seq:
  - "@attr1": value1
  - "@attr2": value2
  - 123
  - abc

Corresponding XML:

<seq attr1="value1" attr2="value2">123</seq>
<seq attr1="value1" attr2="value2">abc</seq>

The aforementioned syntax does not allow to express XML text nodes with XML attributes as YAML. This special case can be achieved using an #text attribute key:

map_key:
  "@attr1": value1
  "#text": value2

Corresponding XML:

<map_key attr1="value1">value2</map>

Implementation Details​

For each config file, the server also generates file-preprocessed.xml files when starting. These files contain all the completed substitutions and overrides, and they are intended for informational use. If ZooKeeper substitutions were used in the config files but ZooKeeper is not available on the server start, the server loads the configuration from the preprocessed file.

The server tracks changes in config files, as well as files and ZooKeeper nodes that were used when performing substitutions and overrides, and reloads the settings for users and clusters on the fly. This means that you can modify the cluster, users, and their settings without restarting the server.