Reading host's env variables from Wasm VMs

[mathetake]

Actually, there's a need for reading envs from Plugins as you can see issues below:

• How to set Environment variables for Envoy-Filter? proxy-wasm-cpp-sdk#32
• How to get envoy environment variables in the Proxy-Wasm extension? tetratelabs/proxy-wasm-go-sdk#102

We should have a consensus on how to deal with it, like,

• having a restriction system to limit which variable can be read from a particular plugin
• just leaving this to the host implementation

this is somewhat related to #17 since this would be implemented as WASI's environ_get.

[xuecanlong]

and do you have plan to support in https://github.com/proxy-wasm/proxy-wasm-rust-sdk ?

[mathetake]

@xuecanlong
once it's specified in ABI, yeah this would be added to Rust SDK for sure. But we haven't reached any consensus yet. So please stay tuned for the ABI update. cc @PiotrSikora

[xuecanlong]

@mathetake
Thanks, I really need it.
Do we have another way to get POD_NAMESPACE and POD DEPLOYMENT NAME?

[PiotrSikora]

Note that there is really nothing for the Proxy-Wasm spec to define here (well, other than saying that it's allowed, see: #17), since reading environment variables is already defined in the WASI spec.

This actually already works in the Rust SDK (if you compile it for the wasm32-wasi target), but we don't export any variables in Envoy, so the list is empty.

@mathetake if you want to add a key-value map of the variables to export from Envoy, feel free to do it. But this has to be an explicit map (possibly with pass-through for configured values) and not a complete pass-through to the host variables.

[mathetake]

@mathetake if you want to add a key-value map of the variables to export from Envoy, feel free to do it. But this has to be an explicit map (possibly with pass-through for configured values) and not a complete pass-through to the host variables.

OK, will do. Thanks for clarification here!

[mathetake]

Created the issue in Envoy side: envoyproxy/envoy#14958. Please refer there for those who are interested in this feature.

[linzg2002]

@mathetake I am very interested on this reading host env feature. So I just reviewed all issues and PR around this topic. But still not very clear about how to use it in real case. Could you give some tips? Such as how to config it in envoy.yaml and how to write the code in the wasm filter in C++?
I actually had tried like this:
in istio envoyfilter.yaml

config:
  root_id: my_root_id
  vm_config:
    code:
      local:
        filename: /var/local/lib/wasm-filters/example-filter.wasm
    runtime: envoy.wasm.runtime.v8
    vm_id: "my_vm_id"
    environment_variables: ["HOME"]

in my wasm-filter.cc

    this->theHome = std::getenv("HOME");

Unluckily, I got nothing output. So anywrong I did on this? Bwt, is the function support by istio-envoy? and which should the istio version to be at least? Looking forward for your help, thanks in advance.

[capitanFlint129]

@linzg2002, it seems to be used like this:

environment_variables:
  host_env_keys: ["HOME"]