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Background Information

For the driver class of org.apache.shardingsphere.driver.ShardingSphereDriver, by implementing the SPI of org.apache.shardingsphere.infra.url.ShardingSphereURLLoader, allows YAML configuration files to be fetched from multiple sources and File Systems and parsed into ShardingSphere. If there is no specific statement, the following implementations all use YAML 1.1 as the YAML writing specification. This does not prevent custom implementations of org.apache.shardingsphere.infra.url.ShardingSphereURLLoader from being manually converted to YAML from files such as XML or JSON.

After parsing and loading the YAML file into ShardingSphere’s metadata, the next behavior will be determined again through the relevant configuration of Mode Configuration. Discuss two situations,

  1. ShardingSphere’s metadata does not exist in the Metadata Repository, and local metadata will be stored in the Metadata Repository.
  2. The metadata of ShardingSphere already exists in the Metadata Repository. Regardless of whether it is the same as the local metadata, the local metadata will be overwritten by the metadata of the Metadata Repository.

For the configuration of the Metadata Repository, please refer to Metadata Repository.

How to load configuration files

Load configuration files from classpath

The configuration file is xxx.yaml. When placeholder-type is none or is not specified, the configuration file format is consistent with YAML configuration. When placeholder-type exists and is not none, the configuration file format is defined in the JDBC URL Parameters section of this article.

Example:

  • jdbc:shardingsphere:classpath:config.yaml
  • jdbc:shardingsphere:classpath:config.yaml?placeholder-type=none
  • jdbc:shardingsphere:classpath:config.yaml?placeholder-type=environment
  • jdbc:shardingsphere:classpath:config.yaml?placeholder-type=system_props

Load configuration file from absolute path

The configuration file is xxx.yaml. When placeholder-type is none or is not specified, the configuration file format is consistent with YAML configuration. When placeholder-type exists and is not none, the configuration file format is defined in the JDBC URL Parameterssection of this article.

Example:

  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml?placeholder-type=none
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml?placeholder-type=environment
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml?placeholder-type=system_props

JDBC URL parameters

For implementations of org.apache.shardingsphere.infra.url.ShardingSphereURLLoader, not all JDBC URL parameters must be parsed, this involves how to implement org.apache.shardingsphere.infra.url.ShardingSphereURLLoader.load().

placeholder-type

There is a placeholder-type attribute for optional loading of configuration files containing dynamic placeholders. The default value of placeholder-type is none. When placeholder-type is set to something other than none, allows setting the value of specific YAML properties via dynamic placeholders in the involved YAML file, and configuring optional default values. The name of a dynamic placeholder and its optional default value are separated by :: and wrapped in the outermost layer by $${ and }.

Discuss two situations,

  1. When the corresponding dynamic placeholder value does not exist, the value of this YAML attribute will be set to the default value on the right side of ::.
  2. When neither the corresponding dynamic placeholder value nor the default value on the right side of :: exists, this attribute will be set to empty.

Single dynamic placeholder

none

The configuration file is xxx.yaml, and the configuration file format is consistent with YAML configuration.

Example：

  • jdbc:shardingsphere:classpath:config.yaml
  • jdbc:shardingsphere:classpath:config.yaml?placeholder-type=none
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml?placeholder-type=none
environment

When loading a configuration file containing environment variables, users need to set placeholder-type to environment, which is commonly used in Docker Image deployment scenarios. The configuration file is xxx.yaml, and the configuration file format is basically the same as YAML configuration.

Assume that the following set of environment variables exists,

  1. The existing environment variable FIXTURE_JDBC_URL is jdbc:h2:mem:foo_ds_1;DB_CLOSE_DELAY=-1;DATABASE_TO_UPPER=false;MODE=MySQL.
  2. The existing environment variable FIXTURE_USERNAME is sa.

Then for the intercepted fragment of the following YAML file,

ds_1:
  dataSourceClassName: com.zaxxer.hikari.HikariDataSource
  driverClassName: $${FIXTURE_DRIVER_CLASS_NAME::org.h2.Driver}
  jdbcUrl: $${FIXTURE_JDBC_URL::jdbc:h2:mem:foo_ds_do_not_use}
  username: $${FIXTURE_USERNAME::}
  password: $${FIXTURE_PASSWORD::}

This YAML snippet will be parsed as,

ds_1:
  dataSourceClassName: com.zaxxer.hikari.HikariDataSource
  driverClassName: org.h2.Driver
  jdbcUrl: jdbc:h2:mem:foo_ds_1;DB_CLOSE_DELAY=-1;DATABASE_TO_UPPER=false;MODE=MySQL
  username: sa
  password:

Example:

  • jdbc:shardingsphere:classpath:config.yaml?placeholder-type=environment
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml?placeholder-type=environment
system_props

When loading a configuration file containing system properties, users need to set placeholder-type to system_props. The configuration file is xxx.yaml, and the configuration file format is basically the same as YAML configuration.

Assume the following set of system properties exists,

  1. The existing system property fixture.config.driver.jdbc-url is jdbc:h2:mem:foo_ds_1;DB_CLOSE_DELAY=-1;DATABASE_TO_UPPER=false;MODE=MySQL.
  2. The existing system property fixture.config.driver.username is sa.

Then for the intercepted fragment of the following YAML file,

ds_1:
  dataSourceClassName: com.zaxxer.hikari.HikariDataSource
  driverClassName: $${fixture.config.driver.driver-class-name::org.h2.Driver}
  jdbcUrl: $${fixture.config.driver.jdbc-url::jdbc:h2:mem:foo_ds_do_not_use}
  username: $${fixture.config.driver.username::}
  password: $${fixture.config.driver.password::}

This YAML snippet will be parsed as,

ds_1:
  dataSourceClassName: com.zaxxer.hikari.HikariDataSource
  driverClassName: org.h2.Driver
  jdbcUrl: jdbc:h2:mem:foo_ds_1;DB_CLOSE_DELAY=-1;DATABASE_TO_UPPER=false;MODE=MySQL
  username: sa
  password:

In real situations, system variables are usually defined dynamically. Assume that none of the above system variables are defined, and there is a YAML file config.yaml containing the above YAML interception fragment, users can refer to the following method to create a DataSource instance using the HikariCP Java API.

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;

import javax.sql.DataSource;

public class ExampleUtils {
    public DataSource createDataSource() {
        HikariConfig config = new HikariConfig();
        config.setDriverClassName("org.apache.shardingsphere.driver.ShardingSphereDriver");
        config.setJdbcUrl("jdbc:shardingsphere:classpath:config.yaml?placeholder-type=system_props");
        try {
            assert null == System.getProperty("fixture.config.driver.jdbc-url");
            assert null == System.getProperty("fixture.config.driver.username");
            System.setProperty("fixture.config.driver.jdbc-url", "jdbc:h2:mem:foo_ds_1;DB_CLOSE_DELAY=-1;DATABASE_TO_UPPER=false;MODE=MySQL");
            System.setProperty("fixture.config.driver.username", "sa");
            return new HikariDataSource(config);
        } finally {
            System.clearProperty("fixture.config.driver.jdbc-url");
            System.clearProperty("fixture.config.driver.username");
        }
    }
}

Example:

  • jdbc:shardingsphere:classpath:config.yaml?placeholder-type=system_props
  • jdbc:shardingsphere:absolutepath:/path/to/config.yaml?placeholder-type=system_props

multiple dynamic placeholders

On top of a single dynamic placeholder, users can use multiple dynamic placeholders in a single line of YAML. When configuring the value of a YAML attribute, if part of the value of the YAML attribute needs to be replaced dynamically, you can implement this by configuring multiple dynamic placeholders.

Assume the following set of environment variables or system properties exists,

  1. The existing environment variable or system property FIXTURE_HOST is 127.0.0.1。
  2. The existing environment variable or system property FIXTURE_PORT is 3306。
  3. The existing environment variable or system property FIXTURE_DATABASE is test。
  4. The existing environment variable or system property FIXTURE_USERNAME is sa。

Then for the intercepted fragment of the following YAML file,

ds_1:
  dataSourceClassName: com.zaxxer.hikari.HikariDataSource
  driverClassName: $${FIXTURE_DRIVER_CLASS_NAME::com.mysql.cj.jdbc.Driver}
  jdbcUrl: jdbc:mysql://$${FIXTURE_HOST::}:$${FIXTURE_PORT::}/$${FIXTURE_DATABASE::}?useUnicode=true&characterEncoding=UTF-8
  username: $${FIXTURE_USERNAME::}
  password: $${FIXTURE_PASSWORD::}

This YAML snippet will be parsed as,

ds_1:
  dataSourceClassName: com.zaxxer.hikari.HikariDataSource
  driverClassName: com.mysql.cj.jdbc.Driver
  jdbcUrl: jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=UTF-8
  username: sa
  password:

Other implementations

For details, please refer to https://github.com/apache/shardingsphere-plugin.