I have a big database (~250GB) in Aurora getting lots of inserts. There's only one instance, so I'd like to create a replica for redundancy. While we are doing nightly snapshots, we would prefer a more fault tolerant system, and it appears that using aurora replicas would provide automatic failover.
My question: What exactly happens when I use the console and create a replica? Will a new instance come up and begin pulling data from the master instance? Could that affect database performance? I'm sure that it will take some time before the replica "catches up" and loads the 250GB; how will I know when it's "finished"?
Don't want to have any downtime, so I'm a bit afraid to push the "create replica" button without knowing what it does...
What exactly happens when I use the console and create a replica?
A new instance is started as part of the cluster, and it has access to the master's data -- or, perhaps more precisely, the cluster's data. All Aurora instances are members of a "cluster," even if it's only a cluster of one master server. Aurora replication, within the same region, is starkly different than MySQL native replication.
Will a new instance come up and begin pulling data from the master instance?
Not really. As described above, the new instance will come up and be able to read from the master's backing store -- it doesn't have its own separate storage.
Aurora runs on 3 sets of 2 copies of the working data, mirrored and replicated across the availability zones in the region. This logical entity is called the Cluster Volume.
The cluster volume spans multiple Availability Zones in a single region, and each Availability Zone contains a copy of the cluster volume data.
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Aurora.Managing.html
(The docs say each AZ contains "a copy," which is true, but it's mirrored.)
Aurora replicas read from this data -- for all practical purposes, synchronously.
Q: How far behind the primary will my replicas to be?
Since Amazon Aurora Replicas share the same data volume as the primary, there is virtually no replication lag. We typically observe lag times in the 10s of milliseconds.
— https://aws.amazon.com/rds/aurora/faqs/
Could that affect database performance?
It shouldn't.
I'm sure that it will take some time before the replica "catches up" and loads the 250GB; how will I know when it's "finished"?
No, it really shouldn't. Once the replica instance becomes accessible, it should be up-to-date, because it's reading the same data from the same place that the master is writing. Metrics related to Aurora replica lag are accessible in the console.
Related
Our current server consisting of an 2x EC2 instances and RDS (Read/Write) database is in Mumbai Region. However I would like to copy everything (2x EC2 & RDS (R/W)) across to Sydney, and other to other regions.
Ideally I would like to replicate the contents in those instances as well.
Does anyone know a quick and easy way of doing this?
Edit 25/01/2019:
However I would like to copy everything including what ever is inside the instances (2x EC2s and the RDSs)
Edit 29/01/2019:
The purpose is to "scale/expand out". I want to have the same infrastructure replicated 1-to-1 (exactly/identically) across various regions.
It is simple!
- For EC2 - you need to create an AMI of those instances then right click on the AMI you've just created and choose "copy AMI" to the designated region.
For RDS
If you just wanna copy data to another region then take a snapshot then copy that snapshot to destination region
If you want to make the RDS replicate to another region continuously then you need to create a read-replica from your RDS instance.
Option for replicating environment depends on how much downtime can you tolerate.
If you are okay with downtime
1. Copy the AMI of EC2 instance and snapshot of RDS to another regions
2. Bring up your new environment.
This is perfect for non critial workload
If this is critical application
1. Copy the AMI of ec2 instance ( I am assuming this would be your web/app instnaces) For real time replication use rsync or robocopy .. or solution like cloudendure .
2. Create a new RDS instance in sydney
3. USE DMS migration tool .. create source and target relationship
4. once insync cut off the relation bring new environment in sydney
As suggested by previous answers for EC2 you can create AMIs and then move the AMI to a different region.
For RDS, you can either create read replicas (and read replicas of read replicas, but beware of latency), read replicas are used to mainly improve read performance of your app.
You can also create a Multi AZ backup which will act as a disaster recovery site. However, note that Multi-AZ is only used in case of a failover. Moreover, Multi-AZ involves Synchronous data copy and read replicas are asynchronous, so read replicas can demonstrate eventual consistency behavior.
But the real question here is - What are you trying to achieve?
Are you trying to "scale out" your infrastructure to support huge traffic to your application? Or are you simply trying to setup disaster recovery (DR)?
If your answer is DR, then the approach is pretty straight forward with Multi AZ and EC2 instance snapshots. But if the answer is scaling out and performance, you really need to be thinking of better strategies such as using Cloudfront (CDN) if it is a web app, using Elasticache in-memory cache for frequently read data, or RDS read replicas, using Elastic Load Balancers with Dynamic/Step scale-out/scale-in. Other, methods would be to evaluate the type of RDS storage subsystem used i.e. using Provisional IOPs vs. Using General Purpose SSD, checking if there are any NAT “instance” bottlenecks in your VPC and so on.
It may be tempting to spin up all these redundant copies of EC2 AMIs or RDS read replicas with a click of a button, but you really need to be thinking about the cost you are going to incur on a monthly basis for completely un-used resources.
I'm trying to evaluate AWS RDS Aurora as future replacement for our local MySQL databases, but I'm noticing some strange behaviors.
I have a basic cluster with a DB master (writer) and a replica (reader). My idea was to use the reader as an always available datasource, even when the writer in unavailable. But when I'm rebooting the master, it takes down the reader as well, making the setup quite worthless.
Looking at the reader replica log, this is what happens when the it notices that the writer is down:
Does anyone know how to have a Aurora read entry point that never goes down even if the writer is offline or busy for a brief time?
Or does the write/read "out of sync" always take down the reader entry points no matter the size of the cluster?
The only way to have a replica that remains available during a reboot of the master would be to have an asynchronous replica using conventional MySQL replication -- which Aurora does support.
Aurora replication is very different than MySQL (or Galera) replication. A loss of the master necessarily triggers a reorganization of the cluster, because the individual instances don't have their own copies of the data, they share a 6-way replicated storage volume -- that's how replication can remain in the 10-20 ms time range. What's actually replicated from the master is the transaction log LSN. Replacement of a master requires one replica to be promoted, verify that the on-disk data structures are clean after taking over, and then all of the other replicas start follow it.
If the DB cluster has one or more Aurora Replicas, then an Aurora Replica is promoted to the primary instance during a failure event. A failure event results in a brief interruption, during which read and write operations fail with an exception.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Aurora.Managing.html#Aurora.Managing.FaultTolerance
When an Aurora replica stops seeing updates from the master, it doesn't matter where the actual fault lies -- whether with the actual master or elsewhere in the infrastructure -- the replica stops serving queries because, best case, it no longer has access to authoritative data.
Where possible, zero-downtime patching appears to avoid a master restart during upgrades. Other than upgrades, there should not be a need to restart the master.
If a primary Aurora DB instance dies for some reason, and an existing replica gets promoted to the new primary, does a new replica instance get created so that I end up with the same number of read replicas?
If so, how long does it take for a new replica to be spun up on average?
There are two types of read replicas:
Backup replica (also known as slave) made by AWS when you deploy Multi-AZ RDS instance. That is synchronous read replica, but you can not use it.
Read replica created by you. Those are asynchronous replicas that you can use to offload some work.
A backup replica will be promoted to master automatically, usually it takes less than a minute. And yes, AWS will create new slave for the RDS instance that's now the master. It could take from several minutes to several hours depending on your workload and DB size.
Read replicas created by you will be just switched to the new master.
AWS Aurora is AWS's database with an architecture designed for cloud computing technologies. One of it's differences is that data is stored in a storage architecture similar to S3, in a cluster volume, which is a single, utilizes solid state disk (SSD) drives and consists of copies of the data across multiple Availability Zones in a single region. That has a few advantages, such as durability and also the fact that is distributed through in entire region, not just an AZ, helping with consistency between replicas and performance.
In case you have read replicas and your Master fails, one of them will become Master without downtime.
If you don't have a read replica, a new Master instance will be created and the process is really fast. Since data is on clusterized across the region, not on the server's disk, the process is fast, but there is downtime.
As AWS says:
To increase availability, you can use Aurora Replicas as failover
targets. That is, if the primary instance fails, an Aurora Replica is
promoted to the primary instance with only a brief interruption during
which read and write requests made to the primary instance fail with
an exception. If your Aurora DB cluster does not include any Aurora
Replicas, then the primary instance is recreated during a failure
event. However, promoting an Aurora Replica is much faster than
recreating the primary instance. For high-availability scenarios, we
recommend that you create one or more Aurora Replicas, of the same DB
instance class as the primary instance, in different Availability
Zones for your Aurora DB cluster. For more information on Aurora
Replicas as failover targets, see Fault Tolerance for an Aurora DB
Cluster.
You can read more on: http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Aurora.Replication.html"
can someone help me with these questions please :
1- the documentation stated that Aurora will automatically fail-over to the read replicas, my question is how does it select the replica which will be promoted if you have more than one with different instances class?
2- can I disable this automatic fail-over (just asking, not stating that I will do it)
3- what is the purpose of multi-az in Aurora if you can have the same effect with much more control on instances classes while creating replicas and let Aurora do the auto fail-over for you. please correct me if I am wrong with this assumption.
thanks in advance
The algorithm for election of a new master in case of failure is not really documented... but it doesn't seem to matter, because Aurora replicas seem to be different than other RDS replicas, because all the instances in the cluster are necessarily of the same instance class.
Unlike other RDS offerings, read replicas in Aurora do not appear to have an independent copy of the backing store -- instead, the backing store itself provides redundancy, being replicated at the storage level with two copies in each of three availability zones.
The cluster volume is made up of multiple copies of the data for the DB cluster, but the data in the cluster volume is represented as a single, logical volume to the primary and Aurora Replicas in the DB cluster.
Because the cluster volume is shared among all instances in your DB cluster, no additional work is required to replicate a copy of the data for each Aurora Replica.
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Aurora.Replication.html
Multi-AZ in Aurora is also not the same thing -- with other RDS products, multi-AZ involves a second, invisible instance, running in parallel with the master. The Aurora literature uses the phrase "multi-AZ technology," but the meaning appears to be different. Note that the Aurora pricing tables don't show a separate pricing rate for "multi-AZ" the way MySQL and MariaDB do.
Failover doesn't appear to be something that can be disabled. Even if you have no replicas, Aurora will still "fail over" if the master fails -- but it does it by spinning up a replacement master using the existing cluster volume as the backing store.
The above answer is no longer valid anymore.
Multi AZ = Aurora Cluster with at least one Read Replica in a
different AZ.
You can still create multiple read replicas for a cluster but if you create them within the same AZ of your writer, cluster will not be multi AZ.
Within each AWS Region, Availability Zones (AZs) represent locations that are distinct from each other to provide isolation in case of outages. We recommend that you distribute the primary instance and reader instances in your DB cluster over multiple Availability Zones to improve the availability of your DB cluster. That way, an issue that affects an entire Availability Zone doesn't cause an outage for your cluster.
You can set up a Multi-AZ cluster by making a simple choice when you create the cluster. The choice is simple whether you use the AWS Management Console, the AWS CLI, or the Amazon RDS API. You can also make an existing Aurora cluster into a Multi-AZ cluster by adding a new reader instance and specifying a different Availability Zone.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Concepts.AuroraHighAvailability.html
When launching an Aurora instance I have the option of "Multi-AZ Deployment", which it describes as "Specifies if the DB Instance should have a standby deployed in another Availability Zone."
However the Aurora documentation states that Aurora already automatically spreads the database across different availability zones?
Additionally, what is the difference between an Aurora Multi-AZ standby and an ordinary Aurora replica. Is that that an ordinary replica can be read from increasing performance whereas a standby cannot be read from?
Aurora replicates your data across three availability zones, at the storage layer... but the database server instance, itself, is still a virtual machine running on a single physical machine that is located in a single availability zone.
The Aurora storage layer is outside that instance, and is able to let access continue uninterrupted without data loss, even in the event of the loss of up to two AZs, but the loss of the zone containing the db instance will still cause an outage for you, if you only have a single Aurora instance in your cluster (1 master, 0 replicas). Loss of an entire availability zone is one of those things that is highly improbable but not impossible. Your db instance is still a single point of failure when you only have one.
Multi-AZ makes allowance for a complete redundant database instance, in a different AZ, which will automatically take over for the primary within one minute, if it works as designed, in case of the loss of the AZ hosting the primary instance or a catastrophic failure of the primary instance. It's a second virtual machine, on a second physical machine, in a second availability zone. It's always running, but you can't access it. It's in the background, managed and monitored by the RDS infrastructure, but it is only accessible to you in the case of primary instance failure. The secondary machine can also be used to reduce downtime in the event of a software upgrade or maintenance event on the primary. When failover occurs, if you are using DNS to connect to your database (as you should), you'll find that the DNS entry is automatically pointed to the secondary.
Contrast this to a read replica, which is accessible all the time and can thus provide a significant performance benefit, by allowing the offloading of reads. Failing over to a replica involves promoting it to become a standalone master (which permanently detaches it from its own former master) and reconfiguring your application to use the alternate endpoint. This, of course, is still faster than recovering from a failure in the master by using a point-in-time snapshot to create a replacement master instance.
https://aws.amazon.com/rds/details/multi-az/
Storage in Aurora is replicated across three availability zones. The database head node is a single instance. So, while your data is spread across multiple targets, the head node is not.
When you enable a multi-AZ deployment, we create an Aurora read replica that is available as a failover target. Any Aurora read replicas you create (up to a max of 15 at this time) are also available as failover targets.
There isn't any meaningful difference between Multi-AZ and other Aurora replicas. This is primarily a simplification in the user interface for customers accustomed to using Multi-AZ for other RDS engines.
AWS Management console.
The answer to this is straightforward.
You can create Multi-AZ in the management console or ignore it. Irrespective, the shared storage for Amazon Aurora is across three AZ (Multi-AZs) as it's the feature of Amazon Aurora however if we choose the Mult-AZ option then we will also have your instances of Amazon Aurora in multiple AZs.
Thus you should choose the Amazon console image option