Issue
rsyslog consumed growing amounts of memory when forwarding over TCP with compression enabled.
*.* @@(z1)hostname.domain.tld
Cause
The compression flag causes the rsyslog process to allocate, and never release, memory. I have not determined root cause but the likely culprits are zlib or TLS (both involved when compression is enabled in this situation).
Resolution
Do not use compression when forwarding with rsyslog. With the compression flag dropped, I was unable to reproduce the errant behavior.
*.* @@hostname.domain.tld