metrics: Use prometheus for process metrics

We currently have our own implementation of system level metrics. This
is unnecessary. The `prometheus` crate provides a _process_ feature that
bundles prometheus's default process-level metrics. This adds a
`process_threads` metric.

This change also updates the static `proxy_build_info` metric to be
exported via the default prometheus registry. This allows us to export
this metric from the top-level `linkerd2-proxy` crate so that the build
metadata is not inferred from the linkerd-app-core crate (fixing an old
TODO).

---

Before

> # HELP process_start_time_seconds Time that the process started (in seconds since the UNIX epoch)
> # TYPE process_start_time_seconds gauge
> process_start_time_seconds 1701551542
> # HELP process_uptime_seconds_total Total time since the process started (in seconds)
> # TYPE process_uptime_seconds_total counter
> process_uptime_seconds_total 1782.137
> # HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.
> # TYPE process_cpu_seconds_total counter
> process_cpu_seconds_total 0.72
> # HELP process_virtual_memory_bytes Virtual memory size in bytes.
> # TYPE process_virtual_memory_bytes gauge
> process_virtual_memory_bytes 111042560
> # HELP process_resident_memory_bytes Resident memory size in bytes.
> # TYPE process_resident_memory_bytes gauge
> process_resident_memory_bytes 33910784
> # HELP process_open_fds Number of open file descriptors.
> # TYPE process_open_fds gauge
> process_open_fds 28
> # HELP process_max_fds Maximum number of open file descriptors.
> # TYPE process_max_fds gauge
> process_max_fds 1048576
> # HELP proxy_build_info Proxy build info
> # TYPE proxy_build_info gauge
> proxy_build_info{version="2.213.0",git_sha="9f7e7ac",profile="release",date="2023-11-16T23:24:26Z",vendor="linkerd"} 1

After:

> # HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.
> # TYPE process_cpu_seconds_total counter
> process_cpu_seconds_total 0
> # HELP process_max_fds Maximum number of open file descriptors.
> # TYPE process_max_fds gauge
> process_max_fds 1048576
> # HELP process_open_fds Number of open file descriptors.
> # TYPE process_open_fds gauge
> process_open_fds 24
> # HELP process_resident_memory_bytes Resident memory size in bytes.
> # TYPE process_resident_memory_bytes gauge
> process_resident_memory_bytes 27656192
> # HELP process_start_time_seconds Start time of the process since unix epoch in seconds.
> # TYPE process_start_time_seconds gauge
> process_start_time_seconds 1701553218
> # HELP process_threads Number of OS threads in the process.
> # TYPE process_threads gauge
> process_threads 2
> # HELP process_uptime_seconds_total Total time since the process started (in seconds)
> # TYPE process_uptime_seconds_total gauge
> process_uptime_seconds_total 9.700919434
> # HELP process_virtual_memory_bytes Virtual memory size in bytes.
> # TYPE process_virtual_memory_bytes gauge
> process_virtual_memory_bytes 109264896
> # HELP proxy_build_info Proxy build info
> # TYPE proxy_build_info gauge
> proxy_build_info{date="2023-12-02T21:32:40Z",git_sha="9a4d02c6f",profile="release",vendor="code@ver-sea",version="0.0.0-dev.9a4d02c6f"} 1

Cargo.lock

@@ -1060,6 +1060,7 @@ dependencies = [
  "linkerd-app-inbound",
  "linkerd-app-outbound",
  "linkerd-error",
+ "linkerd-metrics",
  "linkerd-opencensus",
  "rangemap",
  "regex",
@@ -1135,7 +1136,6 @@ dependencies = [
  "linkerd-stack",
  "linkerd-stack-metrics",
  "linkerd-stack-tracing",
- "linkerd-system",
  "linkerd-tls",
  "linkerd-trace-context",
  "linkerd-tracing",
@@ -1145,7 +1145,6 @@ dependencies = [
  "pin-project",
  "quickcheck",
  "regex",
- "semver",
  "serde_json",
  "thiserror",
  "tokio",
@@ -1623,6 +1622,7 @@ dependencies = [
  "hyper",
  "linkerd-stack",
  "parking_lot",
+ "prometheus",
  "quickcheck",
  "tokio",
  "tracing",
@@ -2010,15 +2010,6 @@ dependencies = [
  "tracing",
 ]
 
-[[package]]
-name = "linkerd-system"
-version = "0.1.0"
-dependencies = [
- "libc",
- "procfs",
- "tracing",
-]
-
 [[package]]
 name = "linkerd-tls"
 version = "0.1.0"
@@ -2132,10 +2123,12 @@ version = "0.1.0"
 dependencies = [
  "futures",
  "jemallocator",
+ "lazy_static",
  "linkerd-app",
  "linkerd-meshtls",
  "linkerd-signal",
  "num_cpus",
+ "semver",
  "tokio",
  "tracing",
 ]
@@ -2559,9 +2552,9 @@ dependencies = [
 
 [[package]]
 name = "procfs"
-version = "0.15.1"
+version = "0.14.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "943ca7f9f29bab5844ecd8fdb3992c5969b6622bb9609b9502fef9b4310e3f1f"
+checksum = "b1de8dacb0873f77e6aefc6d71e044761fcc68060290f5b1089fcdf84626bb69"
 dependencies = [
  "bitflags 1.3.2",
  "byteorder",
@@ -2570,6 +2563,23 @@ dependencies = [
  "rustix 0.36.16",
 ]
 
+[[package]]
+name = "prometheus"
+version = "0.13.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "449811d15fbdf5ceb5c1144416066429cf82316e2ec8ce0c1f6f8a02e7bbcf8c"
+dependencies = [
+ "cfg-if",
+ "fnv",
+ "lazy_static",
+ "libc",
+ "memchr",
+ "parking_lot",
+ "procfs",
+ "protobuf",
+ "thiserror",
+]
+
 [[package]]
 name = "prost"
 version = "0.11.8"
@@ -2678,6 +2688,12 @@ dependencies = [
  "prost 0.12.1",
 ]
 
+[[package]]
+name = "protobuf"
+version = "2.28.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "106dd99e98437432fed6519dedecfade6a06a73bb7b2a1e019fdd2bee5778d94"
+
 [[package]]
 name = "quick-error"
 version = "1.2.3"
@@ -2947,9 +2963,9 @@ dependencies = [
 
 [[package]]
 name = "semver"
-version = "1.0.17"
+version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bebd363326d05ec3e2f532ab7660680f3b02130d780c299bca73469d521bc0ed"
+checksum = "836fa6a3e1e547f9a2c4040802ec865b5d85f4014efe00555d7090a3dcaa1090"
 
 [[package]]
 name = "serde"

Cargo.toml

@@ -60,7 +60,6 @@ members = [
     "linkerd/stack",
     "linkerd/stack/metrics",
     "linkerd/stack/tracing",
-    "linkerd/system",
     "linkerd/tonic-watch",
     "linkerd/tls",
     "linkerd/tls/test-util",

linkerd/app/Cargo.toml

@@ -24,6 +24,7 @@ linkerd-app-gateway = { path = "./gateway" }
 linkerd-app-inbound = { path = "./inbound" }
 linkerd-app-outbound = { path = "./outbound" }
 linkerd-error = { path = "../error" }
+linkerd-metrics = { path = "../metrics", features = ["process"] }
 linkerd-opencensus = { path = "../opencensus" }
 rangemap = "1"
 regex = "1"

linkerd/app/core/Cargo.toml

@@ -73,11 +73,5 @@ version = "0.4"
 default-features = false
 features = ["make", "spawn-ready", "timeout", "util", "limit"]
 
-[target.'cfg(target_os = "linux")'.dependencies]
-linkerd-system = { path = "../../system" }
-
-[build-dependencies]
-semver = "1"
-
 [dev-dependencies]
 quickcheck = { version = "1", default-features = false }

linkerd/app/core/src/lib.rs

@@ -24,7 +24,6 @@ pub mod metrics;
 pub mod proxy;
 pub mod serve;
 pub mod svc;
-pub mod telemetry;
 pub mod transport;
 
 pub use drain;

linkerd/app/core/src/metrics.rs

@@ -11,7 +11,7 @@ use crate::{
     classify::Class,
     control, http_metrics, http_metrics as metrics, opencensus, profiles, stack_metrics,
     svc::Param,
-    telemetry, tls,
+    tls,
     transport::{self, labels::TlsConnect},
 };
 use linkerd_addr::Addr;
@@ -143,14 +143,7 @@ where
 // === impl Metrics ===
 
 impl Metrics {
-    pub fn new(
-        retain_idle: Duration,
-        start_time: telemetry::StartTime,
-    ) -> (Self, impl FmtMetrics + Clone + Send + 'static) {
-        let process = telemetry::process::Report::new(start_time);
-
-        let build_info = telemetry::build_info::Report::default();
-
+    pub fn new(retain_idle: Duration) -> (Self, impl FmtMetrics + Clone + Send + 'static) {
         let (control, control_report) = {
             let m = metrics::Requests::<ControlLabels, Class>::default();
             let r = m.clone().into_report(retain_idle).with_prefix("control");
@@ -212,9 +205,7 @@ impl Metrics {
             .and_report(control_report)
             .and_report(transport_report)
             .and_report(opencensus_report)
-            .and_report(stack)
-            .and_report(process)
-            .and_report(build_info);
+            .and_report(stack);
 
         (metrics, report)
     }