Is there any limit for the number of vpc to be attached to an elastic load balancer in aws. I have created an ELB with one VPC , I wanted to know , whether I can have multiple vpc on the same load balancer?
When setting up an Elastic Load Balancer (ELB) you must specify exactly one VPC. In this VPC you can select one subnet per Availability Zone (AZ).
These settings are needed to assign an IP address to the ELB. When you configure one one subnet then the ELB hat only one IP in this subnet. It is recommended to assign at least two subnets (in different AZs) to the ELB. This way any outage in one AZ does not affect the ELB.
Remember that this configuration is only for input data. Therefore, we handle the question how to connect to the ELB. Configuring output, e.g. where to forward the data by ELB, is another topic.
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I have an elastic beanstalk application which has an ALB and ec2 instances that can be created in any of the 6 AZ's based on the auto scaling policy.
I then put an NLB in front to create a single static IP which seems to work fine as long as at least 1 ec2 instance exists in the same AZ that the NLB lives. If ec2 instances exist only in other AZ's the health check is timing out and the routing isn't working from the NLB anymore. Is the below a possible configuration?
Create Security Group/s that allow traffic between ALB and EC2.
Create SG for EC2 instance to allow traffic from SG
I'll start with describing the architecture of Application Load Balancer:
We have the Application Load Balancer, which contains a list of one or more listeners. Each listener is associated with one specific port and protocol, so that traffic incoming to the load balancer with this port will be handled by this listener. Then, each listener holds a list of rules. A rule specify conditions and actions - basically where to route traffic to. A listener also must have a default action which will be taken if no other condition is met. Usually, this action will be to route traffic to a specific target group.
A target group is a group of either EC2 instances, IP addresses, other Application Load Balancer, or Lambda function.
Furthermore, when you create an Application Load Balancer, it asks you to specify a VPC and list of 2 or more Availability zones, and for each to specify a subnet.
My question now is: Why does AWS asks you to specify this? As far as I understand, the target groups and the registered targets are where you specify the backend of the load balancer, so why do we need to specify the subnets in the ALB configuration?
EDIT
After experimenting, I found that, if I have a EC2 instance running a web server in AZ 3 for example, and now I create a load balancer and selects AZs 1 and 2, then traffic will not reach the web server on AZ 3 until I add another AZ in the load balancer settings.
So if to accurate my question: If this setting of AZs in the load balancer settings means: these are the AZs in which the Load Balancer will send traffic to, in what scenario should I not choose ALL the availability zones there are?
An Application Load Balancer runs on Amazon EC2 infrastructure. Think of it as an Amazon EC2 instance with pre-loaded software, but you don't actually see the EC2 instance in your own account.
Instead, you will see the Network Interfaces where the Load Balancer connects into the network.
Traffic will come into your network through an Internet Gateway then route within the VPC to the Load Balancer. The Load Balancer will then determine a target to receive the traffic, and will send the request via the Network Interface to the resource in the VPC.
When such traffic flows through the VPC, it is subject to normal Security Groups and Network Access Control Lists (NACLs). Private IP addresses will be assigned for each Network Interface used by the Load Balancer.
The Load Balancer instance runs in multiple AZs. If one AZ has a failure, then the Load Balancer instance in the remaining AZ(s) will continue to run. This is why the Load Balancer wants a connection to the VPC in multiple subnets.
Bottom line: While you might normally think of the Load Balancer as a "blackbox service", it is still just some software running on a virtualized computer that needs logical connectivity to the VPC, and it obeys all the rules of networking within the VPC.
why do we need to specify the subnets in the ALB configuration?
Because the load balancer itself requires physical network interfaces, which are created in the subnets you specify (one network interface per subnet).
When you need ALB you must assign an IP address to it. A subnet is nothing more than a range of IP addresses. By placing an ALB inside a subnet, you define which range of IP you desire to be assigned to this resource. Moreover, These subnets allow you to configure different security layers regards the resource inside the subnet for traffic management.
Your target group is located in another subnet with a different range, whereas you can place your ALB in another subnet with a different range.
I am creating a backend with ECS and I need to have a static IP, for what I understand from the AWS console all internet-facing load balancers are assigned an IP address by AWS, my question is: Will that IP address change? And if I have 2 Availability Zones, both have different IPs?
For internet-facing load balancers, the IPv4 addresses of the nodes are assigned by AWS.
For internal load balancers, the IPv4 addresses are assigned from the subnet CIDR.
Yes, the IPs change sporadically and you're correct that the IP is different in each Availability Zone.
If you need to have static IPs, you could consider fronting an Application Load Balancer with a Network Load Balancer. This would allow an elastic IP to be set for each AZ that the NLB resides and you should still get the benefits of the ALB.
The downsides would be extra cost and latency. I haven't tried this myself so can't vouch for how well it works.
Source: https://aws.amazon.com/blogs/networking-and-content-delivery/application-load-balancer-type-target-group-for-network-load-balancer/
Will that IP address change? And if I have 2 Availability Zones, both have different IPs?
Yes, for application load balancer (ALB), the IPs are not static. If you want static IP for ALB you can add AWS Global Accelerator to it.
Alternatively, use network LB (NLB), which has static IP addresses.
When creating a Network Load Balancer, there is the option to allocate an Elastic IP address per AZ from one of the EIPs available to you. If you don't allocate an EIP, AWS assigns a Static IP per AZ that can be used by applications as the front-end IP of the load balancer. Note that this only applies to the NLB.
Source: https://aws.amazon.com/elasticloadbalancing/network-load-balancer/
I've setup an Application Load Balancer in my primary VPC where most of my instances are. I have some instances in another VPC hosting docker services and I want to setup rules to access these at http://domain.com/services/. I have peering enabled between the two VPCs and I've created a target group, but the ALB only lists target groups within its own VPC. Is there any way to access the target group in the peered VPC or am I out of luck? I've been unable to find any leads on google so far. I've made sure the subnets in the ALB have routing through the VPC peering, but that hasn't helped.
You can load balance using ALBs and use the internal IP address of the peered VPC. You can do this via selecting the target type as ip when setting up the Target Group.
Amazon has a great write up on this exact problem and solution: https://aws.amazon.com/blogs/aws/new-application-load-balancing-via-ip-address-to-aws-on-premises-resources/
Since you are going VPC to VPC, substitute their "on premise" wording with "my other VPC". I just set this up using a host header routing for the ALB to cross two VPCs with a single ALB.
try with Route 53 routing policy. you can balance instance beyond the region also.
As far as high availability goes, what is the difference between using an Elastic IP or an Elastic Network Interface to mask instance failure? Is the only difference because ENIs can be used for private instances and Elastic IPs can't?
I'm trying to explain the advantages of both, so if someone can help me with this, I would appreciate it!
To achieve High Availability, you need the ability to redirect traffic in the case of instance failure. There are several options:
1. Use an Elastic Load Balancer
This is the preferred way to provide High Availability.
Run multiple Amazon EC2 instances, preferably in different Availability Zones (AZs). Users connect to the ELB (via the supplied DNS name), which redirects traffic to the EC2 instances. If an instance fails, ELB notices this via regular Health Checks, and will only direct traffic to the healthy instances.
Auto Scaling can be used to create these multiple instances across multiple Availability Zones, and it can also update the Load Balancing service when it adds/removes instances.
2. Redirect an Elastic IP address
Run multiple instances (preferably across multiple Availability Zones). Point an Elastic IP address to the instance you desire. Users connect via the Elastic IP address and are directed to the instance. If the instance fails, reassociate the Elastic IP address to a different instance, which will then start receiving the traffic immediately.
This method is not recommended because only one instance is receiving all the traffic while the other instance(s) are sitting idle. It also requires a mechanism to detect failure and reassociate the Elastic IP (which you must do yourself).
3. Reassign an Elastic Network Interface (ENI)
All EC2 instances have a primary ENI. They can optionally have additional ENIs.
It is possible to direct traffic to a secondary ENI and then move that secondary ENI to another instance. This is similar to reassigning an Elastic IP address.
This method is not recommended for the same reason as reassociating an Elastic IP address (above), but also because an ENI can only be reassigned within the same AZ. It cannot be used to direct traffic to an EC2 instance in a different AZ.
Bottom line: Use an Elastic Load Balancer. It provides true High Availability and can do it automatically.
See documentation: What Is Elastic Load Balancing?