I have the following project structure:

Backend: ASP.NET Core + Redis + Playwright + API (updates prices from LME)
Frontend: Built via build-static.sh, placed in /dist
Dockerfile: A single file that:

• builds the backend

• builds the frontend

• copies the frontend to dist/ and serves it through Nginx

Deployment: A single Railway container service (deployed from GitHub)
Redis: A separate Railway Redis instance in a private network

Below is the relevant Redis configuration code from my Program.cs:
builder.Configuration

.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)

.AddEnvironmentVariables();

var rawRedisUrl = builder.Configuration["ConnectionStrings:Redis"];

Console.WriteLine(" DEBUG: Redis from env = " + rawRedisUrl);

...

if (string.IsNullOrWhiteSpace(rawRedisUrl))

{

throw new InvalidOperationException(" Redis connection string is missing.");

}

try

{

var redisUri = new Uri(rawRedisUrl);

var config = new ConfigurationOptions

{

EndPoints = { $"{redisUri.Host}:{redisUri.Port}" },

Password = redisUri.UserInfo.Split(':')[1],

User = redisUri.UserInfo.Split(':')[0],

AbortOnConnectFail = false,

Ssl = false

};

Console.WriteLine(" Redis connecting...");

var redis = await ConnectionMultiplexer.ConnectAsync(config);

var db = redis.GetDatabase();

try

{

var pong = await db.PingAsync();

Console.WriteLine(" Redis is responsive, latency: " + pong.TotalMilliseconds + "ms");

}

catch (Exception ex)

{

Console.WriteLine(" Redis is not responding:");

Console.WriteLine(ex.ToString());

throw;

}

builder.Services.AddSingleton(redis);

}

catch (Exception ex)

{

Console.WriteLine(" Failed to connect to Redis:");

Console.WriteLine(ex.ToString());

throw;

}

In the Redis service, I added the environment variable:

ConnectionStrings__Redis = ${{REDIS_URL}}

In the technology service, I exposed this variable as:

ConnectionStrings__Redis = ${{Redis.ConnectionStrings__Redis}}

However, during deployment I get an error saying it’s not possible to connect to Redis.
I don’t understand the reason.