zrepl/docs/content/impl/_index.md

+++ title = "Implementation Overview" +++

The following design aspects may convince you that zrepl is superior to a hacked-together shell script solution.

Language

zrepl is written in Go, a real programming language with type safety, reasonable performance, testing infrastructure and an (opinionated) idea of software engineering.

• key parts & algorithms of zrepl are covered by unit tests
• zrepl is noticably faster than comparable shell scripts

RPC protocol

While it is tempting to just issue a few ssh remote 'zfs send ...' | zfs recv, this has a number of drawbacks:

• The snapshot streams need to be compatible.
• Communication is still unidirectional. Thus, you will most likely
  • either not take advantage of features such as compressed send & recv
  • or issue additional ssh commands in advance to figure out what features are supported on the other side.
• Advanced logic in shell scripts is ugly to read, poorly testable and a pain to maintain.

zrepl takes a different approach:

• Define an RPC protocol.
• Establish an encrypted, authenticated, bidirectional communication channel...
• ... with zrepl running at both ends of it.

This has several obvious benefits:

• No blank root shell access is given to the other side.
• Instead, access control lists (ACLs) are used to grant permissions to authenticated peers.
• The transport mechanism is decoupled from the remaining logic, keeping it extensible (e.g. TCP+TLS)

{{% panel %}} Currently, the bidirectional communication channel is multiplexed on top of a single SSH connection. Local replication is of course handled efficiently via simple method calls See TODO for details. {{% / panel %}}