SLA for Virtual Machines
- VMs that have two or more instances deployed across two or more availability zones in the same Azure region, MS guarantee 99.99% of connectivity to at least one instance.
- 99.95% connectivity to at least one instance if VMs deployed in the same availability set or in the same dedicated host group.
- VM using premium SSD for OS and data disk shall have 99.9% connectivity guarantee, 99.5% in case of standard SSD, 95% in case of standard HDD.
It implies that using 2 or more VM leads to 4 9 of availability means 4 min downtime in a month.
Availability Set
The logical grouping of VMs allows Azure to understand how the application is built to provide for redundancy and availability.
There is no cost for the availability set itself, just need to pay for added VM instances.
Fault Domain: physical separation of these virtual machines so that no hardware failure will disrupt both of them.
Update domain
Availability Zone
- Is a physically separate zone, within an Azure region.
- There are three availability zones per Azure region.
- Each availability zone as a distinct power source, network, and cooling.
- It protects applications and data from the loss of data centers.
- If one zone is compromised, then replicated apps and data are instantly available in another zone.
Virtual Machine Scale Set
- Create and manage a group of load-balanced VMs
- The number of VM instances can automatically increase or decrease in response to demand or a defined schedule.
- There is no cost for the scale set itself, you only pay for each VM instance that you create.
- Virtual machines in a scale set can also be deployed into a single Availability zone, or regionally.
Load Balancer
- Combine the Azure Load Balancer with an availability zone or availability set to get the most application resiliency.
- Standard tier virtual machines, the Azure Load Balancer is included.
- Load balancer helps in increasing availability of website and application
- Works at layer 4
- It can also be used to balance the load to containers and PaaS applications
- Global load balancing with Non-HTTPS as recommended traffic
- Supports up to 1000 backend VMs
Azure Firewall
Azure Firewall Manager
Application Gateway
- Works at layer 7
- SSL termination
- Cookie-based session affinity
- Reginal load balancing with HTTPS as recommended traffic
Traffic Manager
- Works at layer 7, DNSs load balancer
- Load balancer for geographically distributed datacenters
- Uses DNS to redirect requests to an appropriate geographical location endpoint
- It Does not see the traffic passing between the client and the service. It simply redirects the request based on the most appropriate endpoints
- Best suitable for load between two endpoints where your first endpoint is in Azure and the second endpoint placed in an on-premise datacenter
- Global LB with Non-HTTPS as recommended traffic
Content Delivery Network (CDN)
- Deliver pages and other Web content to a user, based on the geographic locations of the user, from nearest POP.
Azure FrontDoor
- Works at layer 7
- Offers a single global entry point for customers accessing web apps, APIs, content, and cloud services.
- Global load balancing, but it is doing more by enhancing performance
- Promptly connect to the nearest Front Door POP
- Increase application availability with smart health probes
- URL based routing
- Cookie-based session affinity
- SSL termination
Azure Bastian
- Allows to connect to virtual machine without RDP port open
Notes
- DNS traffic always travel over UDP
- When we update DNS servers in Azure Firewall, it will restart the attached virtual machines.
- If the virtual machine doesn't have public IP address we can RDP to VM using the firewall's public IP.