For Subnets in the same VPC, is Region independent?
I would like to set up more than two fully independent Availability Zones for Elastic Load Balancer(ELB).
Is it possible?
Yes:
Within a Region you create a VPC
The VPC is a logical concept and spans AZs
You then create subnets within the VPC for each AZ
Each AZ is a physically separate datacentre from another, normally 3 AZs or more per region
When you set up an ELB, you select the subnets that you want to use, select a subnet in each AZ
ELB will add instances across all 3 (or more) subnets/AZs
Related
OK I'm trying to create an internal Network Load Balancer.
On the console, it says:
Mappings
Select at least two Availability Zones and one subnet per zone.
And at the same time it also says:
Your internal load balancer must have a private subnet.
I have created a new subnet (NLB-subnet, or subnet subnet-084f41a2d64bd25ad, as shown in the picture above) in my VPC, just for the NLB.
When you create a new subnet, you must choose the zone in which your subnet will reside. And you can only choose one in the AWS console. So I did, and I chose ap-northeast-1a.
However, when it asks me to Select at least two Availability Zones and one subnet per zone., I am confused like a 2 year old:
I have selected the AZ ap-northeast-1a for the NLB mapping, and that's where my new subnet resides, no problem.
But then I have to select a second AZ???
The seconds AZ has no subnet just for the NLB, because you can only choose one AZ for the subnet!
What does it want me to do?
Do I have to create a new private subnet in every one of the 3 Availability Zones, just for the NLB?
what? why?
You don't need to place your NLB in two AZs, if you don't want. NLB works fine in a single AZ as well. Only for ALB it is required to have two AZs. From docs:
You enable one or more Availability Zones for your load balancer when you create it. If you enable multiple Availability Zones for your load balancer, this increases the fault tolerance of your applications.
If ec2 instance is spinned up in an subnet,subnet's NACl rules imply to the instances of that subnet,But where in case of rds, "subnet group" is attached to the rds instance. if I have 2 subnet's in subnet's group. In this scenario, which subnet's NACL rules are applied to the rds ?
When you launch an RDS instance each instance will only be launched in a single subnet, the cluster on the overhand will spread instances across the subnets i.e. read replicas and Multi-AZ.
Each instance if you look at its properties will have availability zone, by using this you can limit down to the availability zone of the host. Assuming you only have a single subnet per AZ in your subnet group you can then identify the subnet.
If you have multiple subnets per AZ you would need to DIG (or ping) the RDS instances hostname to get the IP address. Then you would need to filter to determine which range it is in.
I created two subnets without any preference of the availability zone(AZ). So, now I have two subnets in one AZ. I know that I can extend the VPC and create new subnets but I simply want to move a subnet into a different zone. Is there any way I can move a subnet to a different AZ on AWS?
This is not possible.
An Availability Zone is nominated when the Subnet is created. It is not possible to change the AZ on a Subnet.
You should either create another subnet, or delete the subnet and recreate it in a different AZ.
I'm trying to create an Aurora DB instance using a CloudFormation script. It requires me to have subnets with 2 availability zones. I entered 2 subnets which have different AZs, but now I get this error in the stack creation log:
DatabaseSubnetGroup: Subnet has different VPC Id: vpc-dd3bf9ba than vpc-e0e11ab7.
What does this error mean?
It sounds like the two subnets, although in different availability zones (AZs) are part of two separate VPCs (logical network isolation). You would need to select two subnets in different AZs but in the same VPC.
considering the statement :
When adding an RDS instance to VPC, there needs to be three subnets in
the subnet group across three different AZs for that VPC
what is the difference between three subnets and AZs here?
I know that we need AZs for any RDS instance and it is created automatically by amazon at deployment time. So, this of course means that there should be one subnet in each three AZs to enable access to RDS replicas and instances. Or it means that each AZ should have three subnets created within to enable that?
Amazon provides 99.95% RDS availability
Multi-AZ configurations for MySQL, MariaDB, Oracle, and PostgreSQL are covered by the Amazon RDS Service Level Agreement ("SLA"). The RDS SLA affirms that AWS will use commercially reasonable efforts to make Multi-AZ instances of Amazon RDS available with a Monthly Uptime Percentage of at least 99.95% during any monthly billing cycle.
In order to achieve that database has to be replicated in three different AZ. That is the reason why Amazon requires three subnets in three AZ. The relationship is:
The region has more than one AZ
AZ belongs only to one region
AZ has more than one data center
AZ can have more than one subnets. However, there is a soft limit of 200 subnets per AZ. You can ask Amazon for more than 200 if you need.
Subnet belongs only to one AZ
VPC belongs only to one region. You can have more than one VPC per region. However, there is a soft limit of 5 VPCs per region. You can ask Amazon for more than 5 if you need.
VPC can span more than one AZ.
You can have as many Subnets as you like in each AZ. By default AWS creates one VPC containing one Subnet in each AZ. The number of AZ varies from region to region.
The quote you gave in your question is saying that you must have three subnets, that these three subnets must all be be in different AZ but all three subnets must be in the same VPC.