mirror of
https://github.com/zrepl/zrepl.git
synced 2024-11-23 00:43:51 +01:00
63 lines
2.5 KiB
ReStructuredText
63 lines
2.5 KiB
ReStructuredText
.. _implementation_toc:
|
|
|
|
Implementation Overview
|
|
=======================
|
|
|
|
.. WARNING::
|
|
|
|
Incomplete / under construction
|
|
|
|
The following design aspects may convince you that ``zrepl`` is superior to a hacked-together shell script solution.
|
|
|
|
Testability & Performance
|
|
-------------------------
|
|
|
|
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 (work in progress)
|
|
* 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, an *authenticated* peer can *request* filesystem lists, snapshot streams, etc.
|
|
* Requests are then checked against job-specific ACLs, limiting a client to the filesystems it is actually allowed to replicate.
|
|
* The :ref:`transport mechanism <transport>` is decoupled from the remaining logic, keeping it extensible.
|
|
|
|
Protocol Implementation
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
zrepl implements its own RPC protocol.
|
|
This is mostly due to the fact that existing solutions do not provide efficient means to transport large amounts of data.
|
|
|
|
Package `github.com/zrepl/zrepl/rpc <https://github.com/zrepl/zrepl/tree/master/rpc>`_ builds a special-case handling around returning an ``io.Reader`` as part of a unary RPC call.
|
|
|
|
Measurements show only a single memory-to-memory copy of a snapshot stream is made using ``github.com/zrepl/zrepl/rpc``, and there is still potential for further optimizations.
|
|
|
|
Logging & Transparency
|
|
----------------------
|
|
|
|
zrepl comes with :ref:`rich, structured and configurable logging <logging>`, allowing administators to understand what the software is actually doing.
|