PostgreSQL has supported streaming replication and hot standbys since version 9.0 (2010), and synchronous replication since version 9.1 (2011).
Creation and clean up of WAL files in the primary's pg_wal folder (pg_xlog prior to PG10) is a normal part of PostgreSQL operation. The WAL files on the primary are used to ensure data consistency during crash recovery. Use of write-ahead logs (also called redo logs or transaction logs in other products) is common for data stores that must provide durability and consistency of data when writing to storage. The same technique is used in modern journaling and log-structured filesystems.
pgBouncer is a commonly deployed and recommended connection pooler for PostgreSQL and supports a number of authentication methods including TLS/SSL client certificate authentication.