Proposal for Configuration File Support in Wasmtime

[Mossaka]

Feature

Wasmtime offers flexible configurability through options like the "pooling allocation strategy" and "parallel compilation", which can be set programmatically using the wasmtime::Config struct. To simplify this process and enhance usability, I propose adding support for a configuration file that Wasmtime can consume. This would enable users to configure the engine using a straightforward and centralized file format.

Benefit

Services (such as containerd wasmtime-shim) that uses wasmtime APIs to compile and execute Wasm components today rely on environment variables to configure Wasmtime engine. Whether it is to disable parallel compilation or change the pooling allocation strategy. With the huge number of configuration options that wasmtime provides, it is difficult for users and service providers to maintain these dynamic configuration options. We suggest using a TOML or YAML file for the configuration file due to their readability.

Implementation

1. Parsing Configuration File:
   Implement a parser to read and deserialize the configuration file into a wasmtime::Config struct.

2. Applying Configuration:
   Extend the wasmtime::Config struct with methods to apply settings from the deserialized configuration.

Alternatives

Interestingly, wasmtime CLI has a config command in which you can use it to create a new config.

$ wasmtime config new
Successfully created a new configuration file at '/home/mossaka/.config/wasmtime/config.toml'.

However, this config command is used ONLY for cache configuration, which is a tiny fraction of the total configuration options that wasmtime provides.

[fitzgen]

Extending the existing cache-config TOML for general Wasmtime options makes sense to me.

We probably want to refactor our config and CLI and (now) TOML code such that there is one source of truth that automatically makes knobs for each configurable thing in all those various places.

[pchickey]

This seems like a good idea to me - thanks @Mossaka. Agreed with Nick.

[Mossaka]

Thanks, I might get someone to help with this or do it myself.