Logging it's a must on any application. Making a simmilitude with the journalism when a event appears on our application, we need to answer some questions before writing it This is not strict at all but that i try to say is that an event alone means nothing, we need enrich it with some context. With that a log line will be more usefull:
- Who: Method that generates our event.
- What: Kind of event.
- Where: Context of event, class, request ...
- When: Timestamp of the event.
- Why: Inner exception, data asociated to the event ...
And one thing that i concider very usefull wich is very personal, is that we need wrapping with quotes all parameter that we log, becouse there is a huge difference between this two log lines:
12-12-1988 Warning query paramters id = 12341
12-12-1988 Warning query paramters id = '12341 '
Setup application
I will start with something very simple. The simplest app is a console application, so we create a folder and open a terminal on the folder.
dotnet new console
Add serilog to our csproj and restore packages
<ItemGroup>
<PackageReference Include="Serilog.AspNetCore" Version="3.2.0" />
</ItemGroup>
dotnet restore
My first log
Using serilog is very simple, so next snippet is a fast configuration, you can fount it on the serilog github doc. Let's modify our program.cs
namespace AspnetcoreSerilog
{
class Program
{
static void Main(string[] args)
{
Log.Logger = new LoggerConfiguration()
.MinimumLevel.Debug()
.MinimumLevel.Override("Microsoft", LogEventLevel.Information)
.WriteTo.Console()
.CreateLogger();
Log.Information("Hello world!");
}
}
}
Output of the previous program:
PS D:\Workspace\dev.to\AspnetcoreSerilog> dotnet run
[23:21:53 INF] Hello world!
Configure via appsettings.json
Ok, but serilog's configuration will grow a lot. In a real world app we want a log with a lot of features, subloggers... and if we need changing a configuration section we will need recompile library, we dont want that.
So lets introduce the package serilog-configuration. As a dependency, we will need adding some packages.Reading configuration from a json file can be easly done with microsoft extensions this post may be helpfull. I directly add new dependencies to our csproj:
<ItemGroup>
<PackageReference Include="Serilog.AspNetCore" Version="3.2.0" />
<PackageReference Include="Serilog.Settings.Configuration" Version="3.1.0" />
<PackageReference Include="Microsoft.Extensions.Configuration" Version="3.1.3" />
<PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="3.1.3" />
<PackageReference Include="Microsoft.Extensions.Configuration.CommandLine" Version="3.1.3" />
<PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables " Version="3.1.3" />
</ItemGroup>
<ItemGroup>
<None Update="appsettings.json" CopyToOutputDirectory="PreserveNewest" />
</ItemGroup>
Our program.cs will load configuration and provide it to the logger.
namespace AspnetcoreSerilog
{
class Program
{
static void Main(string[] args)
{
var configuration = new ConfigurationBuilder()
.AddJsonFile("appsettings.json")
.Build();
Log.Logger = new LoggerConfiguration()
.ReadFrom.Configuration(configuration)
.CreateLogger();
Log.Information("Hello world!");
}
}
}
Now, we can configure serilog with via appsettings.json
{
"Serilog": {
"Using": [],
"MinimumLevel": {
"Default": "Debug",
"Override": {
"Microsoft": "Information",
"System": "Warning"
}
},
"WriteTo": [
{ "Name": "Console" }
]
}
}
If we run again the program, output is the same:
PS D:\Workspace\dev.to\AspnetcoreSerilog> dotnet run
[23:24:34 INF] Hello world!
I need customizing output
Serilog output can be easily configured with output template parameter:
{
... Take a look to previous json
"WriteTo": [
{
"Name": "Console",
"Args": {
"outputTemplate": "{Timestamp:dd/MM/yy HH:mm:ss,fff} [{Level:u3}] {Message}{NewLine:1}"
}
}
]
}
}
Output will the following:
PS D:\Workspace\dev.to\AspnetcoreSerilog> dotnet run
04/04/20 23:39:09,387 [INF] Hello world!
This information it´is not enough, i want more. Enrich helps you
There are a lot of enrichers, depending on your needs, you can add its packages to your csproj file. For my example i will use thread enricher:
Add your dependency on csproj and restore:
<PackageReference Include="Serilog.Enrichers.Thread" Version="3.1.0" />
Modify serilog configuration file adding enricher's using and modifying output template to include it:
{
"Serilog": {
"Using": [],
"Enrich":["WithThreadId"],
"MinimumLevel": {...},
"WriteTo": [
{
"Name": "Console",
"Args": {
"outputTemplate": "{Timestamp:dd/MM/yy HH:mm:ss,fff} [{Level:u3}] Thread:{ThreadId} {Message}{NewLine:1}"
}
}
]
}
}
Test output:
PS D:\Workspace\dev.to\AspnetcoreSerilog> dotnet run
04/04/20 23:48:37,002 [INF] Thread:1 Hello world!
Logger it's cool but i need sending my output to various sources
With WriteTo(subloggers) you can send log to any resource, and there are a lot of Sinks already implemented. So the only decisiton you have to take is where you want to place log. For simplicity i will store my log messages in two files and console. So the only sink i need is file sink.
<PackageReference Include="Serilog.Sinks.File" Version="4.1.0" />
Add this 2 nodes to WriteTo section:
{
"Name":"File",
"Args": {
"path": "./log1.log"
}
},
{
"Name":"File",
"Args": {
"path": "./log2.log"
}
}
Output on powershell continue being the same but if we check content of the files will be the same too.
PS D:\Workspace\dev.to\AspnetcoreSerilog> dotnet run
05/04/20 00:01:16,177 [INF] Thread:1 Hello world!
PS D:\Workspace\dev.to\AspnetcoreSerilog> type .\log1.log
2020-04-05 00:01:16.177 +02:00 [INF] Hello world!
PS D:\Workspace\dev.to\AspnetcoreSerilog> type .\log2.log
2020-04-05 00:01:16.177 +02:00 [INF] Hello world!
Information it's duplicate! expressions to the rescue
On a real world app, we will probably need sending logs to diferent files or resources.On this example i will send error logs to one file and information to another. There are a lot of choices for log filtering you can find it here:
First, lets make some changes on our program.cs adding an error log.
namespace AspnetcoreSerilog
{
class Program
{
static void Main(string[] args)
{
// Configuration here
Log.Information("Hello world!");
Log.Warning("Oops!! ");
Log.Error("Ouch!!!! ");
}
}
}
Add package to our csproj:
<PackageReference Include="Serilog.Filters.Expressions" Version="2.1.0" />
Now our json file will change significally, despite of having 2 file sinks we will have 2 subloggers filtered with file sinks. I will show appsettings.json file complete:
{
"Serilog": {
"Using": [
],
"Enrich": [
"WithThreadId"
],
"MinimumLevel": {
"Default": "Debug"
},
"WriteTo": [
{
"Name": "Console",
"Args": {
"outputTemplate": "{Timestamp:dd/MM/yy HH:mm:ss,fff} [{Level:u3}] Thread:{ThreadId} {Message}{NewLine:1}"
}
},
{
"Name": "Logger",
"Args": {
"configureLogger": {
"Filter": [
{
"Name": "ByIncludingOnly",
"Args": {
"expression": "@Level = 'Warning'"
}
}
],
"WriteTo": [
{
"Name": "File",
"Args": {
"path": "./warning.log"
}
}
]
}
}
},
{
"Name": "Logger",
"Args": {
"configureLogger": {
"Filter": [
{
"Name": "ByIncludingOnly",
"Args": {
"expression": "@Level = 'Error'"
}
}
],
"WriteTo": [
{
"Name": "File",
"Args": {
"path": "./error.log"
}
}
]
}
}
}
]
}
}
Output must be the following: Log writes all messages, warning.log file only has warnings logs and error.log only has errors.
PS D:\Workspace\dev.to\AspnetcoreSerilog> dotnet run
05/04/20 00:33:51,927 [INF] Thread:1 Hello world!
05/04/20 00:33:51,948 [WRN] Thread:1 Oops!!
05/04/20 00:33:51,954 [ERR] Thread:1 Ouch!!!!
PS D:\Workspace\dev.to\AspnetcoreSerilog> type .\error.log
2020-04-05 00:33:51.954 +02:00 [ERR] Ouch!!!!
PS D:\Workspace\dev.to\AspnetcoreSerilog> type .\warning.log
2020-04-05 00:33:51.948 +02:00 [WRN] Oops!!
That's all! fell free to leave a comment below!
Resouces
Example repository:
Serilog´s documentation it is enough:
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