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@mastermatt
Last active April 2, 2021 19:47
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Sequel ConnectionWriteableValidator extension
# frozen-string-literal: true
# The connection_writeable_validator extension modifies a Database to validate
# that newly created connections are connected to writeable InnoDB servers.
#
# Based on advise given by Jeremy Evans
# https://groups.google.com/g/sequel-talk/c/JFuxfDuoAZ4/m/hTvgj71uBgAJ
#
# During an Aurora fail over, new connections may resolve to the old primary
# instance, which converts to a ready-only node.
# Checking the `innodb_read_only` global variable allows Sequel::Databases
# to reject the connection if it connects to a read-only instance.
# If rejected, the connection is closed and `connect` is called again on the
# adapter for up to `connect_timeout` seconds.
#
# https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.BestPractices.html
#
#
module Sequel
module ConnectionWriteableValidator
def connect(server)
# The 2 minute default is absurdly high, but it mirrors the default in the Mysql2 gem.
# The expectation is to set a reasonable value in the connection options.
timeout = Float(opts[:connect_timeout] || 120)
timer = Sequel.start_timer
while Sequel.elapsed_seconds_since(timer) < timeout
conn = super(server)
result = conn.query("SHOW GLOBAL VARIABLES LIKE 'innodb_read_only';")
innodb_read_only = (result.first || {})[:Value] != 'OFF'
if innodb_read_only
log_each(:warn, "#{connection_info(conn)}Connected to read-only server. Disconnecting")
disconnect_connection(conn)
next
end
return conn
end
raise DatabaseConnectionError, 'Unable to create a read/write connection'
end
end
Database.register_extension(:connection_writeable_validator, ConnectionWriteableValidator)
end
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