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prometheus-community / prom-label-proxy

A proxy that enforces a given label in a given PromQL query.
Apache License 2.0
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prom-label-proxy

The prom-label-proxy can enforce a given label in a given PromQL query, in Prometheus API responses or in Alertmanager API requests. As an example (but not only), this allows read multi-tenancy for projects like Prometheus, Alertmanager or Thanos.

This proxy does not perform authentication or authorization, this has to happen before the request reaches this proxy, allowing you to use any authN/authZ system you want. The kube-rbac-proxy is an example for such an additional building block. Additionally, you can use prom-label-proxy as a library in your own proxy, like what is done in prom-authzed-proxy.

Risks outside the scope of this project

It's not a goal for this project to solve write tenant isolation for multi-tenant Prometheus:

See Prometheus Operator label enforcement, Thanos soft/hard tenancy or Cortex as example solution to that.

Installing prom-label-proxy

Helm

See: https://github.com/prometheus-community/helm-charts/tree/main/charts/prom-label-proxy

Docker

We publish docker images for each release, see:

Building from source

If you want to build prom-label-proxy from source you would need a working installation of the Go 1.15+ toolchain (GOPATH, PATH=${GOPATH}/bin:${PATH}).

prom-label-proxy can be downloaded and built by running:

go get github.com/prometheus-community/prom-label-proxy

How does this project work?

This application proxies the following endpoints and it ensures that a particular label is enforced in the particular request and response:

When started with the -enable-label-apis flag, the application can also proxy the following endpoints:

You can run prom-label-proxy to enforce the value of the tenant label provided in the client's request via the tenant HTTP query/form parameter:

prom-label-proxy \
   -query-param tenant \
   -label tenant \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080

Accessing the demo Prometheus APIs on http://127.0.0.1:8080 will now expect that the client's request provides the tenant label value using the tenant HTTP query parameter:

➜  ~ curl http://127.0.0.1:8080/api/v1/query\?query="up"
{"error":"The \"tenant\" query parameter must be provided.","errorType":"prom-label-proxy","status":"error"}
➜  ~ curl http://127.0.0.1:8080/api/v1/query\?query="up"\&tenant\="something"
{"status":"success","data":{"resultType":"vector","result":[]}}%

You can provide multiple values for the label using several tenant HTTP query parameters:

➜  ~ curl http://127.0.0.1:8080/api/v1/query\?query="up"\&tenant\="something"\&tenant\="anything"
{"status":"success","data":{"resultType":"vector","result":[]}}%

It also works with POST requests:

➜  ~ curl http://127.0.0.1:8080/api/v1/query" -d "tenant=foo"
{"status":"success","data":{"resultType":"vector","result":[]}}%

Alternatively, prom-label-proxy can use a custom HTTP header instead HTTP parameters:

prom-label-proxy \
   -header-name X-Tenant \
   -label tenant \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080
➜  ~ curl -H 'X-Tenant: something' http://127.0.0.1:8080/api/v1/query\?query="up"
{"status":"success","data":{"resultType":"vector","result":[]}}%

You can provide multiple values for the label using several HTTP headers:

➜  ~ curl -H 'X-Tenant=something' -H 'X-Tenant=anything' http://127.0.0.1:8080/api/v1/query\?query="up"
{"status":"success","data":{"resultType":"vector","result":[]}}%

A last option is to provide a static value for the label:

prom-label-proxy \
   -label tenant \
   -label-value prometheus \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080

Now prom-label-proxy enforces the tenant="prometheus" label in all requests.

You can provide multiple static values for a label. For example:

prom-label-proxy \
   -label tenant \
   -label-value prometheus \
   -label-value alertmanager \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080

prom-label-proxy will enforce the tenant=~"prometheus|alertmanager" label selector in all requests.

You can match the label value using a regular expression with the -regex-match option. For example:

prom-label-proxy \
   -label-value '^foo-.+$' \
   -label namespace \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080 \
   -regex-match

:warning: The above feature is experimental. Be careful when using this option, it may expose sensitive metrics if you use a too permissive expression.

To error out when the query already contains a label matcher that conflicts with the one the proxy would inject, you can use the -error-on-replace option. For example:

prom-label-proxy \
   -header-name X-Namespace \
   -label namespace \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080 \
   -error-on-replace

Once again for clarity: this project only enforces a particular label in the respective calls to Prometheus, it in itself does not authenticate or authorize the requesting entity in any way, this has to be built around this project.

Federate endpoint

The proxy ensures that all selectors passed as matchers to the /federate endpoint must contain that exact match of the particular label (and throws away all other matchers for the label).

Query endpoints

For the two query endpoints (/api/v1/query and /api/v1/query_range), the proxy parses the PromQL expression and modifies all selectors in the same way. The label-key is configured as a flag on the binary and the label-value is passed as a query parameter.

For example, if requesting the PromQL query

http_requests_total{namespace=~"a.*"}

and specifying the namespace label must be enforced to b, then the query will be re-written to

http_requests_total{namespace=~"b"}

This is enforced for any case, whether a label matcher is specified in the original query or not.

Metadata endpoints

Similar to query endpoint, for metadata endpoints /api/v1/series, /api/v1/labels, /api/v1/label/<name>/values the proxy injects the specified label all the provided match[] selectors.

NOTE: When the /api/v1/labels and /api/v1/label/<name>/values endpoints were added to prom-label-proxy, the Prometheus and Thanos endpoints didn't support the match[] parameter hence the prom-label-proxy labels endpoints are disabled by default. Use the -enable-label-apis flag to enable with care. Ensure that the upstream endpoints support label selectors:

Rules endpoint

The proxy requests the /api/v1/rules Prometheus endpoint, discards the rules that don't contain an exact match of the label(s) and returns the modified response to the client.

To return alerting rules which have active alerts matching the label(s), you can use the -rules-with-active-alerts option. For example:

prom-label-proxy \
   -header-name X-Namespace \
   -label namespace \
   -upstream http://demo.do.prometheus.io:9090 \
   -insecure-listen-address 127.0.0.1:8080 \
   -rules-with-active-alerts

Alerts endpoint

The proxy requests the /api/v1/alerts Prometheus endpoint, discards the rules that don't contain an exact match of the label(s) and returns the modified response to the client.

Silences endpoint

The proxy ensures the following:

:rotating_light: prom-label-proxy doesn't support multiple label values for the Silences endpoints :rotating_light:

Example use

The concrete setup being shipped in OpenShift starting with 4.0: the proxy is configured to work with the label-key: namespace. In order to ensure that this is secure is it paired with the kube-rbac-proxy and its URL rewrite functionality, meaning first ServiceAccount token authentication is performed, and then the kube-rbac-proxy authorization to see whether the requesting entity is allowed to retrieve the metrics for the requested namespace. The RBAC role we chose to authorize against is the same as the Kubernetes Resource Metrics API, the reasoning being, if an entity can kubectl top pod in a namespace, it can see cAdvisor metrics (container_memory_rss, container_cpu_usage_seconds_total, etc.).