Modernizing your on-prem SIEM with Microsoft Sentinel – part 1

While an on-premises SIEM (Security Information and Event Management) requires dedicated hardware, storage, maintenance, and is managed by internal IT or security teams and they can be complex to manage, with longer deployment times and higher total cost of ownership.

Have you thought that how you should modernize your SIEM? Is your physical hardware in it’s EOL (end-of-life) and you have need to start thinking to update your current hardware. How about a cloud solution? One good option is to modernize your on-prem SIEM with Microsoft Sentinel.

What is on-prem SIEM?

An on-premises Security Information and Event Management (SIEM) system is a security platform deployed and managed within your organization’s own infrastructure. It collects, analyzes, and correlates log data from various systems and devices to detect security threats, monitor compliance, and support incident response.

In summary you need to:

have a datacenter or some space for your devices
buy racks, servers, network devices, file storage systems or have hypervisor environment like Vmware, Nutanix and build the needed on-prem SIEM vendor setup to those devices.
update devices manually
buy more disk and install them when log space is full.

The idea here is you need to do all things by yourself and manually (or you might have workers to install these) and you need to update them because they get older and might broke randomly. For the setup you need to pay a lot in advance.

After you have your setup done you have to install the siem software and configure it.

And when you have finally got the ready setup you can start thinking and planning to update those on-prem devices with security & OS updated and many more. So lot of work in on-prem.

So why not to start thinking to transfer your on-prem SIEM to automated Cloud SIEM…

What is Microsoft Sentinel?

Microsoft Sentinel is a cloud-native Security Information and Event Management (SIEM) and Security Orchestration, Automation, and Response (SOAR) solution built on Microsoft Azure. It helps organizations detect, investigate, and respond to security threats across their entire digital estate — whether on-premises, in Azure, or across multiple clouds and platforms.

Sentinel leverages AI, machine learning, and threat intelligence to detect, investigate, and respond to threats quickly and efficiently. With built-in automation, seamless integration with Microsoft Defender XDR, and support for multi-cloud and hybrid environments, Sentinel helps modernize SOC operations while reducing infrastructure complexity and total cost of ownership.

It’s a single point, overview of ALL your data sources which could generate alerts and incidents. You can see these in one place. No need to hop in diffenrent solutions and compile the situation status manually when Sentinel does it automatically.

Core capabilities of Microsoft Sentinel

1. Data Collection at Scale

Collects data from cloud, on-premises, and hybrid environments.
Supports a wide range of data connectors (e.g., Microsoft 365, Azure AD, AWS, firewalls, endpoint security tools). Look image below.
Uses Log Analytics Workspace to store and analyze data.

2. Advanced Threat Detection

Once you have your data onboarded, Microsoft Sentinel begins monitoring your entire environment to set baselines and begin identifying behaviors that could indicate issues.

Analytics rule templates are pre-built rule prototypes, designed by Microsoft’s teams of security experts and analysts based on their knowledge of known threats, common attack vectors, and suspicious activity escalation chains.
Supports custom detection rules using Kusto Query Language (KQL).
User entity and behavior analytics (UEBA) is powered by machine learning and helps to generate high fidelity alerts. When enabled, this allows for detection of specific anomalous login behaviors based on IP and geolocation and user history information.
The MITRE ATT&CK framework is a publicly accessible knowledge base of tactics and techniques commonly used by attackers. The dashboard built into sentinel helps users to visualize the nature of your coverage. It allows you to understand how many detections are currently active in your workspace for a specific technique or search for a technique to review your status
Integrates with Microsoft Threat Intelligence to enhance accuracy.
SOC optimization delivers tailored recommendations to help manage security and business requirements
and lot of more

3. Investigation & Hunting

Visual investigation graphs help analysts understand attack paths.
Threat hunting tools allow proactive exploration using KQL queries.
Integrates with MITRE ATT&CK framework for threat context.
Integrates with Microsoft DefenderXDR
Triage investigations to focus on what matters
Automatically assign a severity to each incident, based on Machine Learning that takes into account the number of alerts, the entities impacted, threat intelligence and more.
Provide tags for each incident, to ground analysts in context before even going into an investigation. This includes things such as an attack tactic or whether automatic attack disruption has already taken place.
and more

4. Respond with automation and orchestration (SOAR)

Automation is critical to keeping the SOC ahead of attackers. With built-in SOAR, Microsoft Sentinel delivers a number of different types of automations, available out of the box and fully customizable, to help teams to better do their jobs. We have many different types of playbooks available out of the box that are customizable to your unique needs.

Enrichment automations can help to automatically add more information to your incidents. This can include matching the IP address used in an alert to known threat actors from your TI, helping you get more context as you dig into what happened.

You can automatically integrate with other tools like ServiceNow to ticket incidents in your organization, and get bidirectional updates. This helps make sure you are on track everywhere you are working to respond.

And, you can automate how you respond to an incident by, for example, creating an a list of commands that are taken whenever a specific type of incident, like phishing happens. This can be done automatically, or triggered by a click of a button, reducing the amount of manual work your analysts must do.

Key benefits using Microsoft Sentinel

Benefit	Description
Cloud-native	No hardware or complex setup; scales automatically.
Unified visibility	Centralizes data from across environments.
AI-powered	Reduces false positives and improves detection.
Automated response	Fast, consistent incident handling.
Integration-ready	Works well with Microsoft 365 Defender, third-party security tools, and APIs.

Who should use Sentinel as Cloud SIEM?

Enterprises with hybrid or multi-cloud environments.
Organizations needing real-time threat detection and response.
SOC teams looking to streamline and scale their operations.
Companies aiming to reduce infrastructure and licensing complexity from legacy SIEMs.
Read the FORRESTER post of Total economic impact of using Microsoft Sentinel

Summary

Here was in short what are the advantages of Microsoft Sentinel the cloud siem vs on-prem siem.

In next part I will describe some steps how the transfer is actually done.

Jussi Metso

Author is a lifelong IT enthusiast, Microsoft Security MVP and interested in Cloud Security, XDR, SIEM and AI. Motto: Learning is the key for your future.

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