In a previous post I’ve talked about how you can add logs to Azure Log Analytics. This post is about how you can make use of that logging . The key to Log Analytics (once your log data is in) is its query language.

You can navigate to Log Analytics from the Azure Portal. I’m using Application Insights for the examples and you can get to Log Analytics from the menu bar or by clicking search in the left hand panel and then Log analytics

Once in Log Analytics there will be an area for queries

An area for your data sources

and a query explorer where you can find queries that you or your team have saved previously.

The data sources section is a useful place to start because double clicking a data source will add it to the query. So starting with double clicking “exceptions” the press the Run button. This will query the exceptions logs and return all the exception logs that happening in the last 24 hours (as indicated by the time range next to the run button). If you want to add a time period to your query so that you can use it in a dashboard for example. There are some date functions to help. If you are unsure about how to add query parameters then you can go to the data that is returned and click the plus button next to the item you want to add to your query as below:

This will make the query look as follows:

exceptions

| where timestamp == todatetime('2019-06-26T18:21:49.1473946Z')

This is useful as you can add in >= to the query to find all logs that happened after this time but if you want to get all logs that happened over a specific period you can use the DateTime functions by typing a space after the greater than sign and see a list of the available functions

I use the “ago” function which also has help tips once you select it

As you can see there are examples for minutes, hours and days.

Queries are also built up using the pipe symbol so you can easily append.

If you want to summarise your data so you can get a count of each of the exceptions then you add a new pipe using the summarize keyword and the count function.You need to tell the query which property you wish to count. If you look at the “filter on” screen shot above you will see that there is a type property in the log record. If we summarize that property with count then the query will return all the exceptions in the timeframe and how often they have occurred

The query language also has a use “render” keyword that allows you to return the query in a variety of graphs

So the final query looks like this

exceptions

| where timestamp > ago(70d)

| summarize count() by type

| render piechart

Clicking the save button allows you to save your queries so that you can use them later or share them with other uses who share the same log analytics instance

In my next post I will show how you can use some of the other log tables, ordering and selecting the columns you wish to display

With any key/password store I always thought that the weak link was the credentials used to access it. If that single point of failure was compromised then all your secrets would be vulnerable. Microsoft have overcome this by creating the Managed Identity. A Managed Identity is generated by a resource within Azure and can be configured to access resources that use Azure AD for authentication. As the Managed Identity is generated by the resource there are no credentials to store anywhere and code running in the resource can use this built-in identity to access other resources. This is specifically useful for Key Vault because we can now give access to Key Vault to specific resources without the need to store any credentials anywhere. This post will show you how to access Azure Key vault from an App Service using a Managed Identity to retrieve a secret for use in accessing other services.

So I have a web site deployed to Azure App Service and in order to access Key Vault I need to create a Managed Identity for the App Service. In the Azure Portal navigate to your App Service and click on the Identity blade

Your Manages Identity status should be Off. Click it On and then hit Save. This has now enabled your Managed Identity. The App Service Identity now exists in your associated Azure AD tenant and can be assigned to resources. This means that any code I write and deploy to this App Service will be able to take advantage of this built in identity to access the resources I need. In this example I want to access Key Vault. I therefore need to enable this new user in Key Vault. To do this I need to create a new access policy in Key Vault for this user.

Navigate to your Key Vault and click “Access policies”

Click “Add Access policy”

I’m interesting in just secrets from this Key Vault so I’ve selected the Secret Management template then clicked “None selected”. You should now see a new Principal blade appear. Type the name of you App service in the search box and select the principal that appears. Now click the “Select” button followed by the “Add” button. If you have not done this stage then you will get an error like this, when trying to access the Key Vault:

Service request failed. Status: 403 (Forbidden) The user, group or application 'appid=<app id>;oid=<oid>;iss=https://sts.windows.net/<tenantid>/' does not have secrets get permission on key vault 'yourkeyvault;location=westeurope'.

You should be setup now to access the secrets from code. there is a quick start guide produced by Microsoft to help with this.

Two packages are required to access Key Vault secrets.

Azure.Security.KeyVault.Secrets & Azure.Identity

With the packages installed the code to access Key Vault is simple.

var credential = new DefaultAzureCredential();
var client = new SecretClient(new Uri("https://yourkeyvault.vault.azure.net/"), credential);
var secret = await client.GetSecretAsync("YourSecret");
string actualSecret = secret.Value.Value;

Once this code is deployed to your App Service, the DefaultAzureCredential will automatically pick up the Managed Identity and allow you to access the secrets stored in it. Create a SecretClient, point it at your Key Vault and add the Managed Identity credential. Now you can retrieve the secret and use it.

Managed Identity is another tool to help you make your applications more secure. There is now a reduced risk of compromise from a mishandled Key Vault credential that you’ve stored somewhere safe. The Managed Identity cannot be used from anywhere other than code running in your App Service.