Using Web UI and Expression Browser

1. Accessing Web Interface

Method	Description	Example
Default Address	Local address where Prometheus web UI is accessible	`http://localhost:9090`
Query Parameters	Optional parameters to customize UI behavior	`?g=g1&g=g2`

Example: Starting Prometheus with default UI

prometheus --config.file=prometheus.yml

Note: The web UI is enabled by default when Prometheus is started with a valid configuration file.

Warning: Ensure that the Prometheus server is running and accessible from your browser before attempting to access the web interface.

2. Using Expression Browser

Example: Querying a metric

up

Expression	Description	Notes
up	Boolean indicating if a job is up	Returns 1 for up, 0 for down
rate(up[5m])	Rate of change over 5 minutes	Useful for detecting recent outages

Note: The Expression Browser supports full Prometheus Query Language (PromQL) syntax.

Example: Using functions

rate(http_requests_total[1h])

Function	Description	Usage
rate()	Calculates per-second rate over a time window	`rate(metric[5m])`
sum()	Aggregates values across a vector	`sum(http_requests_total)`
max()	Returns maximum value in a vector	`max(http_requests_total)`

Warning: Expression Browser does not support real-time updates. Results are cached and refreshed on query submission.

Example: Filtering with labels

http_requests_total{job="api-server"}

Label Selector	Example	Description
{job="api-server"}	`http_requests_total{job="api-server"}`	Selects metrics with job label equal to "api-server"
{job!="api-server"}	`http_requests_total{job!="api-server"}`	Selects metrics with job label not equal to "api-server"
{job=~"api.*"}	`http_requests_total{job=~"api.*"}`	Selects metrics with job label matching regex pattern

3. Viewing Targets Status

Target	State	Last Scrape	Scrape Duration	Errors
node_exporter	UP	2026-01-15T10:00:00Z	200ms	0
alertmanager	UP	2026-01-15T10:00:05Z	150ms	0
prometheus	UP	2026-01-15T10:00:10Z	300ms	0
blackbox_exporter	DOWN	2026-01-15T09:55:00Z	—	12

Note: Targets are considered DOWN if they have not been scraped successfully in the last 5 minutes.

Example: Querying Target Status


prometheus_target_status

4. Checking Service Discovery

Example: Service Discovery Configuration

scrape_configs:
  - job_name: "prometheus"
    static_configs:
      - targets: ['localhost:9090']
  - job_name: "node"
    static_configs:
      - targets: ['localhost:9100']
  - job_name: "alertmanager"
    static_configs:
      - targets: ['localhost:9093']

Service Discovery Method	Description	Configuration Example	Notes
Static Config	Manually define targets in configuration	`static_configs:`	Simple and direct, good for small setups
Consul SD	Discover targets via Consul service catalog	`consul_sd_configs:`	Dynamic discovery with service registration
Kubernetes SD	Discover targets from Kubernetes pods/services	`kubernetes_sd_configs:`	Automatically discovers services in cluster
EC2 SD	Discover targets from AWS EC2 instances	`ec2_sd_configs:`	Useful for cloud-based deployments
DNSSD	Discover targets via DNS SRV records	`dns_sd_configs:`	Flexible, supports dynamic updates

Note: Service discovery is critical for dynamic environments where targets may change frequently. Prometheus supports multiple SD methods to integrate with various infrastructure tools.

5. Viewing Configuration

Configuration Item	Description	Example
prometheus.yml	Primary configuration file for Prometheus	`global:`
scrape_configs	Defines how to scrape targets	`scrape_configs: - job_name: 'prometheus' static_configs: - targets: ['localhost:9090']`
rule_files	List of rule files to load	`rule_files: ['alerts.yml']`
storage.tsdb.retention	How long to retain samples in the database	`storage.tsdb.retention: 15d`

Example: Basic Configuration File

global:
  scrape_interval: 15s
  evaluation_interval: 15s

scrape_configs:
  - job_name: 'prometheus'
    static_configs:
      - targets: ['localhost:9090']

Note: The Web UI allows you to view the loaded configuration in YAML format under the Configuration menu.

6. Checking Rule Status

Example: Querying rule status

curl -X GET http://prometheus-server:9090/api/v1/rules

Field	Description	Example Value
name	Rule name	`up:1m`
query	Rule query expression	`up == 1`
labels	Labels applied to rule	`{job="prometheus"}`
state	Current state of rule (active, inactive)	`active`
health	Health status (ok, error)	`ok`

Note: Rule status can be checked via the Prometheus web UI under /rules or through the API endpoint.

Warning: If a rule has health set to error, it indicates a problem with the rule's expression or configuration.

7. Viewing Active Alerts

Field	Description	Example
alertname	Name of the alert rule	`InstanceDown`
job	Job name that triggered the alert	`node_exporter`
instance	Instance that triggered the alert	`node01:9100`
severity	Severity level of the alert	`critical`

Example: Alert Rule Expression


InstanceDown = up == 0

Note: Alerts are displayed in the Web UI under the Alerts tab. Active alerts are those currently firing.

8. Using TSDB Status Page

Example: Accessing TSDB Status Page

curl http://localhost:9090/status

Endpoint	Description	Notes
/status	Provides information about the TSDB (Time Series Database) status	Includes storage statistics, WAL (Write-Ahead Log) info, and compaction stats

TSDB Status Page Overview

Storage Info: Shows the current size of the storage directory and number of series
WAL Info: Displays information about the Write-Ahead Log, including segment count and size
Compaction Info: Lists compaction statistics, including duration and number of chunks
Memory Usage: Shows memory usage statistics for the Prometheus instance

Note: The TSDB status page is available at /status and provides low-level details about the internal state of the Prometheus storage engine.

Warning: This endpoint is intended for debugging and monitoring purposes. It may change in future versions of Prometheus.

9. Checking Runtime Information

Information Type	Description	Endpoint	Notes
Build Information	Version, revision, build date, and Go version of the Prometheus server	`/api/v1/status/buildinfo`	Returns structured JSON with build details
Runtime Information	Process and system-level runtime statistics	`/api/v1/status/runtimeinfo`	Includes memory usage, goroutine count, and GC stats
Config	Current Prometheus configuration file content	`/api/v1/status/config`	Shows loaded config in YAML format
Flags	Command-line flags used to start Prometheus	`/api/v1/status/flags`	Lists all flags and their values

Example: Fetching Build Information

curl "http://localhost:9090/api/v1/status/buildinfo"

Example: Fetching Runtime Info

curl "http://localhost:9090/api/v1/status/runtimeinfo"

10. Using Graph Visualization

Example: Basic Graph Query

up

Expression	Description	Notes
up	Indicates whether a target is up or down	Boolean vector indicating target status
rate(up[5m])	Rate of change over 5 minutes	Useful for detecting target outages

Note: Graphs can be zoomed and panned using mouse controls or keyboard shortcuts.

Example: Query with Labels

http_requests_total{job="prometheus"}

Steps to Visualize Metrics

Navigate to the Graph tab in the Prometheus Web UI
Enter a metric expression in the query input field
Click "Execute" to view results
Adjust time range using the time selector
Use the graph controls to zoom or pan

Graph vs. Table View

Graph: Shows metric values over time with visual trends
Table: Displays raw metric values in tabular format

11. Viewing Command-Line Flags

Flag	Description	Default Value	Notes
--config.file	Path to the configuration file	`prometheus.yml`	Can be overridden with `-c`
--storage.tsdb.path	Directory to store the TSDB data	`data/`	Must be writable by the Prometheus process
--web.listen-address	Address to listen on for web interface and telemetry	`:9090`	Can be changed to bind to a specific IP or port
--web.external-url	External URL to access the Prometheus web UI	`nil`	Used for proper URL generation in alerts and links
--web.enable-lifecycle	Enable reload via HTTP POST to `/-/reload`	`false`	Useful for automated configuration reloads
--web.enable-admin-api	Enable access to admin HTTP API endpoints	`false`	Includes `/-/quit`, `/-/reload`
--storage.tsdb.retention.time	How long to retain samples in the database	`15d`	Can be specified as `h`, `d`, `w`, `y`
--storage.tsdb.min-block-duration	Minimum size of the block in time	`2h`	Used to optimize query performance
--storage.tsdb.max-block-duration	Maximum size of the block in time	`2d`	Used to optimize query performance
--web.console.libraries	Directories to load console libraries from	`nil`	Allows custom dashboard templates to be loaded
--web.console.templates	Directory to load console templates from	`nil`	Used to override default console templates

Example: Starting Prometheus with custom flags

prometheus --config.file="custom.yml" --web.listen-address=":9091" --storage.tsdb.retention.time=30d

12. Accessing Health Endpoints

Endpoint	Description	Response Format	Notes
/-/healthy	Indicates if the Prometheus server is healthy	Text/plain	Returns "ok" if healthy
/-/ready	Indicates if the Prometheus server is ready to serve requests	Text/plain	Returns "ok" if ready
/metrics	Exposes Prometheus metrics in Prometheus text format	Text/plain	Used for scraping by Prometheus or other monitoring systems

Example: Checking Health Endpoints

curl http://localhost:9090/-/healthy
curl http://localhost:9090/-/ready
curl http://localhost:9090/metrics