Connection url with multiple hosts is not supported

[legoethals]

Bug Report

Versions

• io.r2dbc:r2dbc-spi:0.8.2.RELEASE
• io.r2dbc:r2dbc-pool:0.8.3.RELEASE
• io.r2dbc:r2dbc-postgresql:0.8.4.RELEASE

Current Behavior

When a connection url with multiple hosts, e.g. r2dbc:postgresql://host1:5432,host2:5432/db_name, is used for setup through spring application properties, connections cannot be made to the given hosts. An exception is thrown instead: io.r2dbc.postgresql.PostgresqlConnectionFactory$PostgresConnectionException: Cannot connect to host1:5432,host2:5432:5432

Example configuration

spring.r2dbc.url=r2dbc:postgresql://host1:5432,host2:5432/db_name
spring.r2dbc.username=user
spring.r2dbc.password=password

Expected behavior/code

According to the spec, the authority part of the url can contain multiple hosts. I would expect a connection to be made to the first host, and if this connection fails, an attempt is made to connect to the next host in the list, moving on until a connection has been made successfully, or until there is no next host to try.

Possible Solution

Provide actual support for multiple hosts with failover capabilities. This would require quite some changes in the ConnectionUrlParser, ConnectionFactoryOptions, ConnectionFactoryProvider implementation and a
ConnectionFactory implementation that supports failover.

[mp911de]

When parsing a connection url, then multiple hosts are parsed into the host option (see ConnectionUrlParserUnitTests). Whether a driver support multiple hosts or just a single one is up to the actual driver.

Adding a link to the Postgres R2DBC issue for reference: pgjdbc/r2dbc-postgresql#120.

That being said, there's nothing we can do about individual driver feature sets on the specification level.

[kotoant]

Here is the solution, that works without any changes in ConnectionUrlParser, ConnectionFactoryOptions, ConnectionFactoryProvider implementation. It also works with any driver (not only postgresql).

pgjdbc/r2dbc-postgresql#120 (comment)