容器化C# Web API连接Redis缓存失败问题排查

问题描述 #

容器化部署的C# Web API无法连接Redis，报错信息如下：

"No connection is active/available to service this operation: EVAL; UnableToConnect on http://localhost:6379:6379/Interactive, Initializing/NotStarted, last: NONE, origin: BeginConnectAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 60s, state: Connecting, mgr: 10 of 10 available, last-heartbeat: never, global: 0s ago, v: 2.2.4.27433, mc: 1/1/0, mgr: 10 of 10 available, clientName: d252797b3b96, IOCP: (Busy=0,Free=1000,Min=1,Max=1000), WORKER: (Busy=1,Free=32766,Min=8,Max=32767), v: 2.2.4.27433\n at StackExchange.Redis.ConnectionMultiplexer.ExecuteSyncImpl[T](Message message, ResultProcessor1 processor, ServerEndPoint server) in /_/src/StackExchange.Redis/ConnectionMultiplexer.cs:line 2798\n at StackExchange.Redis.RedisBase.ExecuteSync[T](Message message, ResultProcessor1 processor, ServerEndPoint server) in //src/StackExchange.Redis/RedisBase.cs:line 54\n at StackExchange.Redis.RedisDatabase.ScriptEvaluate(String script, RedisKey[] keys, RedisValue[] values, CommandFlags flags) in //src/StackExchange.Redis/RedisDatabase.cs:line 1189\n at Microsoft.Extensions.Caching.StackExchangeRedis.RedisCache.Set(String key, Byte[] value, DistributedCacheEntryOptions options)\n at Program.<>c.<$>b__0_1(String name, String val, IDistributedCache cache) in /src/Program.cs:line 25"

非容器环境下连接Redis正常，相关配置代码如下：

Program.cs #

builder.Services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = builder.Configuration["RedisConnection"];
});

docker-compose.yaml #

version: "3.7"
services:
  web-api:
    build: ./WebAPI
    image: webapi
    container_name: api
    ports:
      - "3000:80"
    environment:
      - RedisConnection=http://localhost:6379
    depends_on:
      - cache
  cache:
    image: redis
    container_name: redis_cache
    ports:
      - "6379:6379"

问题根源 #

容器内的localhost指向容器自身，而非宿主机或Redis容器。当前配置中Web API容器尝试连接自身的6379端口，自然无法访问到独立的Redis容器。此外，StackExchange.Redis的连接字符串不需要http://前缀，该前缀会导致连接解析错误。

修复步骤 #

1. 修正Redis连接字符串
   修改docker-compose.yaml中Web API的环境变量，将RedisConnection的值改为Redis服务的名称cache（Docker Compose会自动为服务创建内部DNS解析），同时去掉无效的http://前缀：

   environment:
     - RedisConnection=cache:6379
   

2. 添加Redis健康检查（可选）
   depends_on仅保证Redis容器先启动，但不确保Redis服务完全就绪。添加健康检查可让Web API等待Redis服务可用后再启动：

   cache:
     image: redis
     container_name: redis_cache
     ports:
       - "6379:6379"
     healthcheck:
       test: ["CMD", "redis-cli", "ping"]
       interval: 5s
       timeout: 3s
       retries: 5
   web-api:
     build: ./WebAPI
     image: webapi
     container_name: api
     ports:
       - "3000:80"
     environment:
       - RedisConnection=cache:6379
     depends_on:
       cache:
         condition: service_healthy
   

3. 重启容器服务
   执行以下命令重新部署容器：

   docker-compose down && docker-compose up -d
   

内容的提问来源于stack exchange，提问作者Pedro