# Apollo Config — Distributed Configuration Management Center

> Apollo is a reliable configuration management system for distributed microservices, providing centralized config management, real-time push, versioning, and gray releases.

## Install

Save as a script file and run:

# Apollo Config — Distributed Configuration Management Center

## Quick Use
```bash
# Start Apollo via Docker Compose
git clone https://github.com/apolloconfig/apollo.git
cd apollo
docker compose -f docker-compose.yml up -d
# Access portal at http://localhost:8070
# Default credentials: apollo / admin
```

## Introduction
Apollo is a configuration management center developed by Ctrip (Trip.com Group) for distributed systems. It centralizes application configuration across environments and clusters, enabling real-time config pushes without restarting services. Apollo is widely adopted in production by organizations running Java-based microservice architectures.

## What Apollo Config Does
- Centralizes configuration for multiple applications, environments, and clusters in a single portal
- Pushes configuration changes to clients in real time (typically under 1 second)
- Tracks full version history of every configuration change with rollback support
- Supports gray releases to push config changes to specific instances before full rollout
- Provides namespace-based config isolation with inheritance and override capabilities

## Architecture Overview
Apollo follows a three-tier architecture: the Config Service handles config reading and real-time push via long polling, the Admin Service manages config modifications through the Portal, and the Meta Server acts as a service discovery layer. Clients maintain a local cache for resilience against network failures. Eureka is embedded for internal service registration, and a MySQL database stores all configuration data, audit logs, and release history.

## Self-Hosting & Configuration
- Requires Java 8+ runtime and MySQL 5.7+ for persistent storage
- Deploy Config Service, Admin Service, and Portal as separate processes for production
- Configure `server.properties` with database connection strings and Eureka endpoints
- Use environment variables or `-D` JVM flags to set per-environment Meta Server addresses
- Docker and Kubernetes Helm charts are available for containerized deployments

## Key Features
- Multi-environment management (DEV, FAT, UAT, PRO) from a single dashboard
- Access control with per-namespace permissions and operation audit logging
- Open API for programmatic config management and CI/CD integration
- Client-side caching ensures applications continue running even if Apollo is temporarily unavailable
- Supports multiple config formats including properties, XML, JSON, YAML, and plain text

## Comparison with Similar Tools
- **Spring Cloud Config** — Git-backed and simple but lacks a management UI, real-time push, and gray release capabilities
- **Consul KV** — Lightweight key-value store with watches, but no versioning, rollback, or structured namespace model
- **etcd** — Low-level distributed KV store best for infrastructure config rather than application-level settings
- **Nacos** — Combines service discovery and config with a similar feature set, but Apollo has a more mature permission and release workflow

## FAQ
**Q: Does Apollo support non-Java applications?**
A: Yes. Apollo provides an Open API and clients for Go, Python, Node.js, PHP, and .NET in addition to its native Java client.

**Q: How does Apollo handle config changes during a deployment?**
A: Config changes are pushed in real time via long polling. Applications receive updates without restarting. For staged rollouts, use the gray release feature to target specific instances.

**Q: Can Apollo run in Kubernetes?**
A: Yes. Official Helm charts are available, and the community maintains Kubernetes-native deployment guides with ConfigMap integration.

**Q: What happens if the Apollo server goes down?**
A: Clients cache the last-known configuration locally. Applications continue operating with cached values until the server recovers.

## Sources
- https://github.com/apolloconfig/apollo
- https://www.apolloconfig.com/

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Source: https://tokrepo.com/en/workflows/asset-8cfde72e
Author: Script Depot