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introduce LaunchTimestamp to identify process restarts

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This patch adds a LaunchTimestamp type to the `metrics` crate,
along with a `libmetric_` Prometheus metric.

The initial user is pageserver.
In addition to exposing the Prometheus metric, it also reproduces
the launch timestamp as a header in the API responses.

The motivation for this is that we plan to scrape the pageserver's
/v1/tenant/:tenant_id/timeline/:timeline_id/layer
HTTP endpoint over time. It will soon expose access metrics (#3496)
which reset upon process restart. We will use the pageserver's launch
ID to identify a restart between two scrape points.

However, there are other potential uses. For example, we could use
the Prometheus metric to annotate Grafana plots whenever the launch
timestamp changes.
This commit is contained in:
Christian Schwarz
2023-02-02 15:46:26 +01:00
committed by Christian Schwarz
parent be81db21b9
commit 87cd2bae77
8 changed files with 112 additions and 7 deletions
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10
pageserver/src/http/routes.rs
View File

@@ -3,6 +3,7 @@ use std::sync::Arc;
use anyhow::{anyhow, Context, Result};
use hyper::StatusCode;
use hyper::{Body, Request, Response, Uri};
use metrics::launch_timestamp::LaunchTimestamp;
use pageserver_api::models::DownloadRemoteLayersTaskSpawnRequest;
use remote_storage::GenericRemoteStorage;
use tokio_util::sync::CancellationToken;
@@ -921,6 +922,7 @@ async fn handler_404(_: Request<Body>) -> Result<Response<Body>, ApiError> {
pub fn make_router(
conf: &'static PageServerConf,
launch_ts: &'static LaunchTimestamp,
auth: Option<Arc<JwtAuth>>,
remote_storage: Option<GenericRemoteStorage>,
) -> anyhow::Result<RouterBuilder<hyper::Body, ApiError>> {
@@ -937,6 +939,14 @@ pub fn make_router(
}))
}
router = router.middleware(
endpoint::add_response_header_middleware(
"PAGESERVER_LAUNCH_TIMESTAMP",
&launch_ts.to_string(),
)
.expect("construct launch timestamp header middleware"),
);
macro_rules! testing_api {
($handler_desc:literal, $handler:path $(,)?) => {{
#[cfg(not(feature = "testing"))]