diff options
Diffstat (limited to 'tvix/docs/components.md')
| -rw-r--r-- | tvix/docs/components.md | 160 |
1 files changed, 0 insertions, 160 deletions
diff --git a/tvix/docs/components.md b/tvix/docs/components.md deleted file mode 100644 index a7d61948c2fa..000000000000 --- a/tvix/docs/components.md +++ /dev/null @@ -1,160 +0,0 @@ ---- -title: "Tvix - Architecture & data flow" -numbersections: true -author: -- adisbladis -- flokli -- tazjin -email: -- adis@blad.is -- mail@tazj.in -lang: en-GB -classoption: -- twocolumn -header-includes: -- \usepackage{caption, graphicx, tikz, aeguill, pdflscape} ---- - -# Background - -We intend for Tvix tooling to be more decoupled than the existing, -monolithic Nix implementation. In practice, we expect to gain several -benefits from this, such as: - -- Ability to use different builders -- Ability to use different store implementations -- No monopolisation of the implementation, allowing users to replace - components that they are unhappy with (up to and including the - language evaluator) -- Less hidden intra-dependencies between tools due to explicit RPC/IPC - boundaries - -Communication between different components of the system will use -gRPC. The rest of this document outlines the components. - -# Components - -## Coordinator - -*Purpose:* The coordinator (in the simplest case, the Tvix CLI tool) -oversees the flow of a build process and delegates tasks to the right -subcomponents. For example, if a user runs the equivalent of -`nix-build` in a folder containing a `default.nix` file, the -coordinator will invoke the evaluator, pass the resulting derivations -to the builder and coordinate any necessary store interactions (for -substitution and other purposes). - -While many users are likely to use the CLI tool as their primary -method of interacting with Tvix, it is not unlikely that alternative -coordinators (e.g. for a distributed, "Nix-native" CI system) would be -implemented. To facilitate this, we are considering implementing the -coordinator on top of a state-machine model that would make it -possible to reuse the FSM logic without tying it to any particular -kind of application. - -## Evaluator - -*Purpose:* Eval takes care of evaluating Nix code. In a typical build -flow it would be responsible for producing derivations. It can also be -used as a standalone tool, for example, in use-cases where Nix is used -to generate configuration without any build or store involvement. - -*Requirements:* For now, it will run on the machine invoking the build -command itself. We give it filesystem access to handle things like -imports or `builtins.readFile`. - -To support IFD, the Evaluator also needs access to store paths. This -could be implemented by having the coordinator provide an interface to retrieve -files from a store path, or by ensuring a "realized version of the store" is -accessible by the evaluator (this could be a FUSE filesystem, or the "real" -/nix/store on disk. - -We might be okay with running the evaluator with filesystem access for now and -can extend the interface if the need arises. - -## Builder - -*Purpose:* A builder receives derivations from the coordinator and -builds them. - -By making builder a standardised interface it's possible to make the -sandboxing mechanism used by the build process pluggable. - -Nix is currently using a hard-coded -[libseccomp](https://github.com/seccomp/libseccomp) based sandboxing -mechanism and another one based on -[sandboxd](https://www.unix.com/man-page/mojave/8/sandboxd/) on macOS. -These are only separated by [compiler preprocessor -macros](https://gcc.gnu.org/onlinedocs/cpp/Ifdef.html) within the same -source files despite having very little in common with each other. - -This makes experimentation with alternative backends difficult and -porting Nix to other platforms harder than it has to be. We want to -write a new Linux builder which uses -[OCI](https://github.com/opencontainers/runtime-spec), the current -dominant Linux containerisation technology, by default. - -With a well-defined builder abstraction, it's also easy to imagine -other backends such as a Kubernetes-based one in the future. - -The environment in which builds happen is currently very Nix-specific. We might -want to avoid having to maintain all the intricacies of a Nix-specific -sandboxing environment in every builder, and instead only provide a more -generic interface, receiving build requests (and have the coordinator translate -derivations to that format). [^1] - -To build, the builder needs to be able to mount all build inputs into the build -environment. For this, it needs the store to expose a filesystem interface. - -## Store - -*Purpose:* Store takes care of storing build results. It provides a -unified interface to get store paths and upload new ones, as well as querying -for the existence of a store path and its metadata (references, signatures, …). - -Tvix natively uses an improved store protocol. Instead of transferring around -NAR files, which don't provide an index and don't allow seekable access, a -concept similar to git tree hashing is used. - -This allows more granular substitution, chunk reusage and parallel download of -individual files, reducing bandwidth usage. -As these chunks are content-addressed, it opens up the potential for -peer-to-peer trustless substitution of most of the data, as long as we sign the -root of the index. - -Tvix still keeps the old-style signatures, NAR hashes and NAR size around. In -the case of NAR hash / NAR size, this data is strictly required in some cases. -The old-style signatures are valuable for communication with existing -implementations. - -Old-style binary caches (like cache.nixos.org) can still be exposed via the new -interface, by doing on-the-fly (re)chunking/ingestion. - -Most likely, there will be multiple implementations of store, some storing -things locally, some exposing a "remote view". - -A few possible ones that come to mind are: - -- Local store -- SFTP/ GCP / S3 / HTTP -- NAR/NARInfo protocol: HTTP, S3 - -A remote Tvix store can be connected by simply connecting to its gRPC -interface, possibly using SSH tunneling, but there doesn't need to be an -additional "wire format" like the Nix `ssh(+ng)://` protocol. - -Settling on one interface allows composition of stores, meaning it becomes -possible to express substitution from remote caches as a proxy layer. - -It'd also be possible to write a FUSE implementation on top of the RPC -interface, exposing a lazily-substituting /nix/store mountpoint. Using this in -remote build context dramatically reduces the amount of data transferred to a -builder, as only the files really accessed during the build are substituted. - -# Figures - - - -[^1]: There have already been some discussions in the Nix community, to switch - to REAPI: - https://discourse.nixos.org/t/a-proposal-for-replacing-the-nix-worker-protocol/20926/22 |