Introduction

Seq is an application which lets you view and analyse logs. It's a great tool for debugging and monitoring your application. In this post I'll cover how I set up Seq to log my ASP.NET Core application. Can never have too many dashboards :)

Setting up Seq

Seq comes in a couple of flavours. You can either use the cloud version or self host it. I chose to self host it as I wanted to keep my logs private.

First I started by visiting the Seq website and finding the Docker install instructions.

Locally

To run locally you first need to get a hashed password. You can do this by running the following command:

echo '<password>' | docker run --rm -i datalust/seq config hash

To run it locally you can use the following command:

docker run --name seq -d --restart unless-stopped -e ACCEPT_EULA=Y -e SEQ_FIRSTRUN_ADMINPASSWORDHASH=<hashfromabove> -v C:\seq:/data -p 5443:443 -p 45341:45341 -p 5341:5341 -p 82:80 datalust/seq

On my Ubuntu local machine I made this into an sh script:

#!/bin/bash
PH=$(echo 'Abc1234!' | docker run --rm -i datalust/seq config hash)

mkdir -p /mnt/seq
chmod 777 /mnt/seq

docker run \
  --name seq \
  -d \
  --restart unless-stopped \
  -e ACCEPT_EULA=Y \
  -e SEQ_FIRSTRUN_ADMINPASSWORDHASH="$PH" \
  -v /mnt/seq:/data \
  -p 5443:443 \
  -p 45341:45341 \
  -p 5341:5341 \
  -p 82:80 \
  datalust/seq

Then

chmod +x seq.sh
./seq.sh

This will get you up and running then go to http://localhost:82 / http://<machineip>:82 to see your seq install (default admin password is the one you entered for above.

In Docker

I added seq to my Docker compose file as follows:

  seq:
    image: datalust/seq
    container_name: seq
    restart: unless-stopped
    environment:
      ACCEPT_EULA: "Y"
      SEQ_FIRSTRUN_ADMINPASSWORDHASH: ${SEQ_DEFAULT_HASH}
    volumes:
      - /mnt/seq:/data
    networks:
      - app_network

Note that I have a directory called /mnt/seq (for windows, use a windows path). This is where the logs will be stored.

I also have a SEQ_DEFAULT_HASH environment variable which is the hashed password for the admin user in my .env file.

Setting up ASP.NET Core

As I use Serilog for my logging it's actually pretty easy to set up Seq. It even has docs on how to do this here.

Basically you just add the sink to your project:

dotnet add package Serilog.Sinks.Seq

I prefer to use appsettings.json for my config so I just have the 'standard' setup in my Program.cs:

builder.Host.UseSerilog((context, configuration) =>
{
    configuration.ReadFrom.Configuration(context.Configuration);
    Serilog.Debugging.SelfLog.Enable(Console.Error);
    Console.WriteLine($"Serilog Minimum Level: {configuration.MinimumLevel.ToString()}");
});

Then in my `appsettings.json' I have this configuration

  "Serilog": {
    "Using": ["Serilog.Sinks.Console", "Serilog.Sinks.File", "Serilog.Sinks.Seq"],
    "MinimumLevel": "Warning",
    "WriteTo": [
        {
          "Name": "Seq",
          "Args":
          {
            "serverUrl": "http://seq:5341",
            "apiKey": ""
          }
        },
      {
        "Name": "Console"
      },
      {
        "Name": "File",
        "Args": {
          "path": "logs/applog-.txt",
          "rollingInterval": "Day"
        }
      }

    ],
    "Enrich": ["FromLogContext", "WithMachineName"],
    "Properties": {
      "ApplicationName": "mostlylucid"
    }
  }

You'll see that I have a serverUrl of http://seq:5341. This is because I have seq running in a docker container called seq and it's on port 5341. If you're running it locally you can use http://localhost:5341. I also use API key so I can use the key to specify the log level dynamically (you can set a key to only accept a certain level of log messages).

You set it up in your seq instance by going to http://<machine>:82 and clicking on the settings cog in the top right. Then click on the API Keys tab and add a new key. You can then use this key in your appsettings.json file.

Docker Compose

Now we have this set up we need to configure our ASP.NET application to pick up a key. I use a .env file to store my secrets.

SEQ_DEFAULT_HASH="<adminpasswordhash>"
SEQ_API_KEY="<apikey>"

Then in my docker compose file I specify that the value should be injected as an environment variable into my ASP.NET app:

services:
  mostlylucid:
    image: scottgal/mostlylucid:latest
    ports:
      - 8080:8080
    restart: always
    labels:
        - "com.centurylinklabs.watchtower.enable=true"
    env_file:
      - .env
    environment:
      - Auth__GoogleClientId=${AUTH_GOOGLECLIENTID}
      - Auth__GoogleClientSecret=${AUTH_GOOGLECLIENTSECRET}
      - Auth__AdminUserGoogleId=${AUTH_ADMINUSERGOOGLEID}
      - SmtpSettings__UserName=${SMTPSETTINGS_USERNAME}
      - SmtpSettings__Password=${SMTPSETTINGS_PASSWORD}
      - Analytics__UmamiPath=${ANALYTICS_UMAMIPATH}
      - Analytics__WebsiteId=${ANALYTICS_WEBSITEID}
      - ConnectionStrings__DefaultConnection=${POSTGRES_CONNECTIONSTRING}
      - TranslateService__ServiceIPs=${EASYNMT_IPS}
      - Serilog__WriteTo__0__Args__apiKey=${SEQ_API_KEY}
    volumes:
      - /mnt/imagecache:/app/wwwroot/cache
      - /mnt/markdown/comments:/app/Markdown/comments
      - /mnt/logs:/app/logs
    networks:
      - app_network

Note that the Serilog__WriteTo__0__Args__apiKey is set to the value of SEQ_API_KEY from the .env file. The '0' is the index of the WriteTo array in the appsettings.json file.

Caddy

Note for both Seq and my ASP.NET app I've specified they both belong to my app_network network. This is because I use Caddy as a reverse proxy and it's on the same network. This means I can use the service name as the URL in my Caddyfile.

{
    email [email protected]
}
seq.mostlylucid.net
{
   reverse_proxy seq:80
}

http://seq.mostlylucid.net
{
   redir https://{host}{uri}
}

So this is able to map seq.mostlylucid.net to my seq instance.

Conclusion

Seq is a great tool for logging and monitoring your application. It's easy to set up and use and integrates well with Serilog. I've found it invaluable in debugging my applications and I'm sure you will too.