Configuring High Availability

1. Running Multiple Prometheus Instances

Example: Configuring HA with two Prometheus instances

# prometheus-1.yml
global:
  scrape_interval: 15s

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

# prometheus-2.yml
global:
  scrape_interval: 15s

scrape_configs:
  - job_name: "prometheus"
    static_configs:
      - targets: ["localhost:9091"]

Configuration	Description	Notes
prometheus.config.file	`prometheus.yml`	Path to the main configuration file
storage.tsdb.path	`data/`	Directory to store the TSDB data
web.listen-address	`:9090`	Address to listen on for web interface and HTTP endpoints
storage.tsdb.retention.time	`2d`	How long to retain samples in the database

Note: For true high availability, you should use a storage backend like Thanos or Cortex to share data between instances.

2. Using Thanos for HA

Example: Basic Thanos Setup

# Prometheus config with Thanos sidecar
prometheus:
  hosts:
    - prometheus-1:9090
    - prometheus-2:9090

thanos:
  sidecar:
    listen: 0.0.0.0:10901
    prometheus_url: http://localhost:9090
    grpc_listen: 0.0.0.0:10902

Component	Description	Notes
thanos.sidecar	Runs alongside Prometheus to expose data via gRPC	Required for HA setup
thanos.store	Stores and serves aggregated metrics from multiple Prometheus instances	Can be deployed in distributed mode
thanos.query	Query engine that can query across multiple Thanos instances	Provides unified query interface

Note: Thanos requires a storage backend (e.g., S3, GCS) for long-term retention.

Thanos vs Native Prometheus HA

Thanos: Distributed, scalable, supports long-term storage
Native HA: Simple replication, limited storage options

Thanos HA Setup Workflow

Deploy Prometheus instances in separate regions or zones
Run Thanos sidecar on each Prometheus instance
Deploy Thanos Store and Query components
Configure query routing to use Thanos Query

3. Implementing Deduplication

Prometheus supports deduplication to prevent duplicate metric samples from being stored or reported, which can occur in high availability setups with multiple instances.

Configuration Option	Description	Default Value	Notes
--deduplication	Enables deduplication of samples across instances	false	Requires `--enable-feature=deduplication` to be enabled
--deduplication.timeout	Timeout for deduplication operations	5m	Time to wait before considering a sample as duplicate

Example: Enabling Deduplication

prometheus --enable-feature=deduplication --deduplication=true --deduplication.timeout=10m

Note: Deduplication is an experimental feature and may not be stable in all environments.

Warning: Enabling deduplication can introduce latency to sample ingestion due to the additional processing required.

4. Configuring Load Balancing

Example: Load Balancer Configuration

# Example HAProxy configuration for Prometheus
global
    daemon
    maxconn 4096

defaults
    mode http
    timeout connect 5s
    timeout client 30s
    timeout server 30s

frontend prometheus_frontend
    bind *:9090
    balance roundrobin
    server prometheus1 10.0.1.10:9090 check
    server prometheus2 10.0.1.11:9090 check
    server prometheus3 10.0.1.12:9090 check

backend prometheus_backend
    balance roundrobin
    server prometheus1 10.0.1.10:9090 check
    server prometheus2 10.0.1.11:9090 check
    server prometheus3 10.0.1.12:9090 check

Load Balancer	Configuration	Notes
haproxy	`balance roundrobin`	Round-robin load balancing algorithm
nginx	`upstream`	Define group of servers to balance
AWS ELB	`Target Groups`	Define target instances for load balancing

Note: Ensure all Prometheus instances in the load balanced setup are configured with identical data sources and configurations to maintain consistency.

Warning: Load balancing Prometheus instances can lead to data inconsistency if not properly configured with shared storage or consistent state management.

5. Using Remote Storage for HA

For high availability in Prometheus, remote storage can be used to store metrics data across multiple systems. This ensures that if one Prometheus instance fails, another can continue to serve metrics from the remote storage.

Storage Type	Description	HA Considerations	Notes
Remote Write	Writes metrics to a remote endpoint	Multiple Prometheus instances can write to the same remote storage	Supports deduplication and sharding
Remote Read	Reads metrics from a remote endpoint	Can be used to query data across multiple Prometheus instances	Supports querying from multiple sources

Example: Configuring Remote Write

remote_write:
  - url: http://remote-storage.example.com/api/v1/write
    queue_config:
      capacity: 10000
      max_shards: 10

Example: Configuring Remote Read

remote_read:
  - url: http://remote-storage.example.com/api/v1/read
    name: "prometheus"

Note: Ensure that the remote storage system is highly available and can handle the write and read load from multiple Prometheus instances.

6. Implementing Alert Deduplication

Configuration Option	Description	Default Value	Notes
alertmanager.timeout	Timeout for sending alerts to Alertmanager	`10s`	Used to prevent long waits during alert deduplication
alertmanager.http.config	HTTP client configuration for Alertmanager	`{}`	Can include TLS settings and timeouts for deduplication
alertmanager.alerts.deduplication	Enable or disable alert deduplication	`true`	Ensures duplicate alerts are not sent to Alertmanager

Example: Alertmanager Configuration with Deduplication

alertmanager:
  timeout: 10s
  http_config:
    tls_config:
      insecure_skip_verify: false
  alerts:
    deduplication: true

Note: Alert deduplication is critical in high-availability setups to prevent alert storms and reduce noise.

7. Setting Up Cross-Region Replication

Configuring cross-region replication in Prometheus involves setting up multiple Prometheus instances in different regions to ensure high availability and data redundancy. This setup allows for failover capabilities and improved query performance by reducing latency.

Component	Description	Configuration
replica	Identifier for the replica instance	`"prometheus-1"`
region	Region identifier for the instance	`"us-west-1"`
remote_write	Configuration for writing data to remote endpoints	`{ "url": "http://remote-prometheus:9090/api/v1/write", "queue_config": { "capacity": 1000, "max_samples_per_send": 1000 } }`
remote_read	Configuration for reading data from remote endpoints	`{ "url": "http://remote-prometheus:9090/api/v1/read", "read_recent": true }`

Example: Remote Write Configuration

remote_write:
  - url: http://prometheus-remote-write:9090/api/v1/write
    queue_config:
      capacity: 1000
      max_samples_per_send: 1000

Example: Remote Read Configuration

remote_read:
  - url: http://prometheus-remote-read:9090/api/v1/read
    read_recent: true

Note: Ensure that all instances in the cross-region setup have consistent configuration to maintain data integrity and avoid discrepancies.

Warning: Cross-region replication introduces additional network latency and potential data synchronization issues. Monitor the replication process regularly to ensure data consistency.

8. Using Consistent Hashing

Prometheus supports consistent hashing for high availability setups to ensure that metrics are distributed evenly across instances.

Configuration Option	Description	Values
--hashmod	Enables consistent hashing for sharding	`true` or `false`
--shard.count	Number of shards to use for consistent hashing	Integer value
--shard.key	Key used for consistent hashing	String (e.g., `instance`)

Example: Configuring Consistent Hashing

prometheus --hashmod=true --shard.count=3 --shard.key=instance

Note: Consistent hashing ensures that when new instances are added or removed, only a minimal number of metrics need to be remapped.

9. Implementing Health Checks

Check Type	Description	Configuration	Notes
HTTP Probe	Checks Prometheus endpoint status via HTTP	`http_get:`	Use for basic liveness/readiness checks
TCP Probe	Verifies Prometheus can connect to a TCP port	`tcp_connect:`	Use for checking service availability
Script Probe	Runs custom script to determine health	`exec:`	Allows complex logic for custom checks

Example: HTTP Probe Configuration

scrape_configs:
  - job_name: 'prometheus'
    http_sd_configs:
      - url: 'http://localhost:9090/targets'
    metrics_path: /metrics
    scrape_interval: 15s
    http_get:
      url: 'http://localhost:9090/health'
      timeout: 5s

Example: TCP Probe Configuration

scrape_configs:
  - job_name: 'prometheus'
    tcp_connect:
      host: 'localhost'
      port: 9090
    scrape_interval: 15s

Note: Health checks should be lightweight to avoid impacting Prometheus performance.

10. Monitoring HA Setup

Example: HA Setup Overview

# prometheus-ha.yml
global:
  evaluation_interval: 1m
  scrape_interval: 15s

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

rule_files:
  - "alerts.yml"

alerting:
  alertmanagers:
    - static_configs:
        - targets:
            - "alertmanager1:9093"
            - "alertmanager2:9093"

Component	Description	Configuration
prometheus	Primary monitoring instance	`scrape_configs`, `alerting`
alertmanager	Alert routing and notification	`alertmanagers` in `prometheus.yml`

Note: Ensure both Prometheus and Alertmanager instances are configured with identical rules and targets for consistency.

HA Monitoring Workflow

Deploy Prometheus in active-passive or active-active mode
Configure Alertmanager cluster with shared storage
Set up cross-instance service discovery (e.g., Consul, DNS)
Monitor instance health via Prometheus metrics

HA Modes Comparison

Active-Passive: One instance active, others standby
Active-Active: All instances handle traffic simultaneously

11. Handling Split-Brain Scenarios

Note: Split-brain scenarios occur when a Prometheus cluster loses network connectivity and splits into isolated groups, each believing it has the complete dataset. This can lead to data inconsistency and duplicate alerts.

Scenario	Description	Impact	Solution
Network Partition	Cluster nodes lose connectivity to each other but remain connected to clients.	Data inconsistency, duplicate alerts, partial query results.	Implement quorum-based decision making or use a consensus protocol like Raft to ensure only one cluster can make decisions.
Node Failure	A node in the cluster becomes unreachable due to hardware or software failure.	Loss of data availability, potential data loss if not properly replicated.	Use replication and automatic failover mechanisms to maintain availability and data integrity.

Example: Configuring Quorum in Prometheus

prometheus:
  global:
    evaluation_interval: 1m
    scrape_interval: 15s
  rule_files:
    - "rules.yml"
  alerting:
    alertmanagers:
      - static_configs:
          - targets:
              - "alertmanager:9093"
  remote_write:
    - url: "http://prometheus-remote-write:9090/api/v1/write"
      queue_config:
        capacity: 1000
        max_samples_per_send: 1000
        batch_send_deadline: 5s

Best Practices for Split-Brain Prevention

Use a consensus protocol like Raft to ensure only one cluster can make decisions during network partitions.
Implement proper replication and failover mechanisms to maintain data availability.
Monitor cluster health regularly to detect and address network issues before they cause splits.

12. Implementing Failover Strategies

Strategy	Description	Implementation	Notes
Active-Passive	One Prometheus instance is active, others are standby	`prometheus --config.file=prometheus.yml \ --storage.tsdb.path=data/active \ --web.listen-address=:9090`	Requires external tooling for failover
Active-Active	All instances are active and handle traffic	`prometheus --config.file=prometheus.yml \ --storage.tsdb.path=data/active1 \ --web.listen-address=:9091`	Requires load balancing and consistent storage
Multi-Region	Instances in different regions for disaster recovery	`prometheus --config.file=prometheus.yml \ --storage.tsdb.path=data/multi-region \ --web.listen-address=:9090`	Use cross-region replication for data consistency

Example: Active-Passive Setup

# Primary instance
prometheus --config.file=prometheus-primary.yml \
  --storage.tsdb.path=data/primary \
  --web.listen-address=:9090

# Standby instance
prometheus --config.file=prometheus-standby.yml \
  --storage.tsdb.path=data/standby \
  --web.listen-address=:9091

Note: Failover requires coordination with external tools like Consul or Kubernetes for automatic switching.

Warning: Inconsistent data may occur if failover happens before replication completes.