Ztunnel provides an experimental implementation of the ztunnel component of ambient mesh.

Note: istio/ztunnel is currently intended for experimental usage only.

Ztunnel is intended to be a purpose built implementation of the node proxy in ambient mesh. Part of the goals of this included keeping a narrow feature set, implementing only the bare minimum requirements for ambient. This ensures the project remains simple and high performance.

Explicitly out of scope for ztunnel include:

• Terminating user HTTP traffic
• Terminating user HTTP traffic (its worth repeating)
• Generic extensibility such as ext_authz, WASM, linked-in extensions, Lua, etc.

In general, ztunnel does not aim to be a generic extensible proxy; Envoy is better suited for that task. If a feature is not directly used to implement the node proxy component in ambient mesh, it is unlikely to be accepted.

Ztunnel's TLS is built on rustls.

Rustls has support for plugging in various crypto providers to meet various needs (compliance, performance, etc).

In all options, only TLS 1.3 with cipher suites TLS13_AES_256_GCM_SHA384 and TLS13_AES_128_GCM_SHA256 is used.

With the boring option, the FIPS version is used. Please note this only implies the specific version of the library is used; FIPS compliance requires more than just using a specific library.

FIPS has strict requirements to ensure that compliance is granted only to the exact binary tested. FIPS compliance was granted to an old version of BoringSSL that was tested with Clang 12.0.0.

Given that FIPS support will always have special environmental build requirements, we currently we work around this by vendoring OS/arch specific FIPS-compliant binary builds of boringssl in

We vendor FIPS boringssl binaries for

• linux/x86_64
• linux/arm64

To use these vendored libraries and build ztunnel for either of these OS/arch combos, for the moment you must manually edit .cargo/config.toml and change the values of BORING_BSSL_PATH and BORING_BSSL_INCLUDE_PATH under the [env] key to match the path to the vendored libraries for your platform, e.g:

BORING_BSSL_PATH = { value = "vendor/boringssl-fips/linux_x86_64", force = true, relative = true }
BORING_BSSL_INCLUDE_PATH = { value = "vendor/boringssl-fips/include/", force = true, relative = true }

BORING_BSSL_PATH = { value = "vendor/boringssl-fips/linux_arm64", force = true, relative = true }
BORING_BSSL_INCLUDE_PATH = { value = "vendor/boringssl-fips/include/", force = true, relative = true }

Once that's done, you should be able to build:

cargo build

This manual twiddling of environment vars is not ideal but given that the alternative is prefixing cargo build with these envs on every cargo build/run, for now we have chosen to hardcode these in config.toml - that may be revisited in the future depending on local pain and/or evolving boring upstream build flows.

Note that the Dockerfiles used to build these vendored boringssl builds may be found in the respective vendor directories, and can serve as a reference for the build environment needed to generate FIPS-compliant ztunnel builds.