Ztunnel

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

Feature Scope

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.

The details of architecture is here.

Building

Please use the same Rust version as the build-tools image. You can determine the version that the build-tools image uses by running the below command:

$ BUILD_WITH_CONTAINER=1 make rust-version

TLS/Crypto provider

Ztunnel's TLS is built on rustls.

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

Name	How To Enable
ring	Default (or --features tls-ring)
boring	--features tls-boring --no-default-features

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

boring FIPS

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:

For linux/x86_64

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 }

For linux/arm64

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.

A release build with this option can be built with TLS_MODE=boring ./scripts/release.sh.

Development

Please refer to this.

Metrics

Ztunnel exposes a variety of metrics, at varying levels of stability. They are accessible by making an HTTP request to either "/stats/prometheus" or "/metrics" on port 15020.

Core metrics are considered stable APIs.

Unstable metrics may be changed. This includes removal, semantic changes, and label changes.

Core metrics

Traffic metrics

• Tcp Bytes Sent (istio_tcp_sent_bytes_total): This is a COUNTER which measures the size of total bytes sent during response in case of a TCP connection.
• Tcp Bytes Received (istio_tcp_received_bytes_total): This is a COUNTER which measures the size of total bytes received during request in case of a TCP connection.
• Tcp Connections Opened (istio_tcp_connections_opened_total): This is a COUNTER incremented for every opened connection.
• Tcp Connections Closed (istio_tcp_connections_closed_total): This is a COUNTER incremented for every closed connection.

Meta metrics

• Istio build information (istio_build)

Unstable metrics

DNS metrics

• DNS Requests (istio_dns_requests_total)
• DNS Upstream Requests (istio_dns_upstream_requests_total)
• DNS Upstream Failures (istio_dns_upstream_failures_total)
• DNS Upstream Request Duration (istio_dns_upstream_request_duration_seconds)
• On Demand DNS Requests (istio_on_demand_dns_total)

In-Pod metrics

• Active proxy count (istio_active_proxy_count_total)
• Pending proxy count (istio_pending_proxy_count_total)
• Proxies started (istio_proxies_started_total)
• Proxies stopped (istio_proxies_stopped_total)

XDS metrics

• XDS Connection terminations (istio_xds_connection_terminations_total)

Logging

Ztunnel exposes a variety of logs, both operational and "access logs".

Logs are controlled by the RUST_LOG variable. This can set all levels, or a specific target. For instance, RUST_LOG=error,ztunnel::proxy=warn. Logs can be emitted in JSON format with LOG_FORMAT=json. Access logs are under the access target.

An example access log looks like (with newlines for readability; the real logs are on one line):

2024-04-11T15:38:42.182974Z  INFO access: connection complete
    src.addr=10.244.0.24:46238 src.workload="shell-6d8bcd654d-t88gp" src.namespace="default" src.identity="spiffe://cluster.local/ns/default/sa/default"
    dst.addr=10.244.0.42:15008 dst.hbone_addr=10.96.108.116:80 dst.service="echo.default.svc.cluster.local"
    direction="outbound" bytes_sent=67 bytes_recv=490 duration="13ms"

Access logs are emitted upon completion of each connection. Logs for connect establishment are also logged (with less information) at debug level.

Currently, the access log format is considered unstable and subject to changes.