So just a quick summary of what we are doing to put everything into context. We have a socket server running as an Azure Cloud Service (worker role) within the South Central US region. All of our other components (Queue, DBs, web app, API etc) are located in East US. The reasons being is sadly due to not being able to modify the static IP address that was created for the South Central US a few years ago. The devices in the field cannot alter their IP as well :/ So we are stuck communicating cross region.
So what Im asking, is there a way to improve latency? Can we "port forward" ? What other options do we have? Im assuming the latency is our biggest enemy here as we pipe data back and forth.
Looking at load balancing at moment - https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-overview
Thoughts?
Load Balancer is a regional service and cannot direct traffic across regions.
There are a couple of options:
1) build your own VM's with a TCP proxy to achieve your scenario. You could use Load Balancer to scale and protect your TCP proxy instance if you want to pursue that path.
2) explore using Application Gateway for this scenario since it is a proxy and can direct to IP address destinations. This is essentially a managed service for option 1, although limited to HTTP & HTTPS.
3) migrate to a DNS approach for locating your service and orchestrating a migration across regions over time.
Either way, traffic would remain on Microsoft's own backbone between regions.
Best regards,
Christian
I am planning to use Azure Traffic manager to do a failover of my app running on one Azure zone to Azure zone.
I need some suggestion, if that is the correct approach to do a failover ? We have seen issue with Azure that, most of the services in one region goes down for few hours. Although I understand that Azure traffic manager is not associated with the region. But is it possible that Azure traffic manager goes down or that traffic manager endpoint is not reachable although my backend webapp is reachable?
If I am planning to use Azure traffic manager, what are other problems I should be worried about ?
I've been working with TM for some time now, so here are a few issues I haven't seen mentioned before:
Keep-Alive
If your service allows Keep-Alive, then your DNS entry will be ignored as long as the connection remains open. I've seen some exceptionally odd behavior result from this, including users being stuck on a fallback page since they kept using the connection, causing it to remain open indefinitely. If you have access to IIS Manager, you can force Keep-Alive to be false.
Browser DNS Caching
Most browsers have their own DNS cache, and very few honor DNS Time To Live. In my experience Chrome is pretty responsive, with IE and Edge having significant delays if you need them to rollover quickly. I've heard that Opera is particularly bad.
Other DNS Caching
Even if you're not accessing your service through a browser, other components can have DNS caches, and some of them will allow you to manage the cache yourself. This can in theory even depend on ISP's DNS caching, though reports on the magnitude of this vary significantly.
Traffic Manager works at the DNS level, which itself is replicated. However, even then, you should still build in redundancy into your solution.
Take a look at the Azure Architecture Center under "Make all things redundant" and you will see a recommendation for Traffic Manager:
consider adding another traffic management solution as a failback. If
the Azure Traffic Manager service fails, change your CNAME records in
DNS to point to the other traffic management service.
The Traffic Manager internal architecture is resilient to the failure of any single Azure region. So, even if a region fails, Traffic Manager should stay up. That applies to all Traffic Manager components: control plane, endpoint monitoring, and DNS name servers.
Since Traffic Manager works at the DNS level, it doesn't have an 'endpoint' that proxies your traffic--it uses DNS to direct clients to the appropriate endpoint, and clients then connect to those endpoints directly. Thus, an unreachable endpoint is an application problem, not a Traffic Manager problem.
That said, if the Traffic Manager DNS name servers are down, you have a serious problem. You DNS resolution path will fail and your customers will be impacted. The only solution is to either accept the risk (small, but can never be zero) or have a plan in place to use another DNS system, either in parallel or failover. This is not a limitation of Traffic Manager; you could say the same about any DNS-based traffic management system.
The earlier answer from DornaDigital is very good (other than the first point which suggests DNS caching will protect you through a name server outage--it won't). It covers some important points. In short, DNS-based failover works well for new sessions. Existing clients may have to refresh or even close their browser and reconnect.
I also agree with the details provided dornadigital.
There are considerations for front end applications as well. The browsers all have different thresholds for how long they maintain persistent connections. Chromium, for example, currently maintains a connection unless there is inactivity for 300 seconds.
In our web applications, we are detecting the failover by the presence of a certain number of failed requests to the endpoint. After requests begin failing, we pause requests for 301 seconds to allow the connection to reset. This allows the DNS change from the traffic manager to be applied to subsequent requests. We pop up a snackbar to indicate to the user that we are having an issue and display the count down when requests will resume. Similar to Gmail when it has an issue connecting to their servers.
I hope that gives you one idea on how to build some redundancy into your web apps.
I disagree with Jonathan as his understanding of the resiliency of the Traffic Manager service is in disagreement with Microsoft's own documentation on the subject.
When you provision Azure Traffic Manager, you select a region in which to deploy the service. I (correctly) inferred this to assert if said region were to fail, the Traffic Manager service could also be impacted and in turn, your application solution would not properly fail over to the secondary region.
According to Microsoft's Azure Application Architecture Guide, under "Make all things redundant", a customer should deploy Traffic Manager into more than one region:
Include redundancy for Traffic Manager. Traffic Manager is a possible failure point. Review the Traffic Manager SLA, and determine whether using Traffic Manager alone meets your business requirements for high availability. If not, consider adding another traffic management solution as a failback. If the Azure Traffic Manager service fails, change your CNAME records in DNS to point to the other traffic management service.
Azure Application Architecture Guide - Make all things redundant
My thought and intention is to not deploy Traffic Manager within the primary service region, but instead to deploy it into the secondary (failover region) and a tertiary (3rd) region as a backup.
At the moment, we are using Azure Traffic Management to provide Load Balancing and High Availability across multiple regions for Azure App Services deployed on App Service Environments. We have reduced the Traffic Manager TTL to 30 secs. However, some of the clients have DNS cache (4 hours TTL) which we cannot control and this impacts the availability of our solution.
What would be a good alternative to provide HA and LB to Azure App Services which does not rely on DNS? We have seen on the documentation that MS suggests third-party solutions, but are there any particular suggestions?
Thanks,
As you point out, Azure Traffic Manager operates in the DNS layer. If you are looking at managing multiple endpoints for high availability and load balancing outside of DNS layer, I would recommend considering Azure Application Gateway (for HTTP workloads) and / or Azure Load Balancer (for any layer 4 (TCP, UDP) load balancing).
You may also find this article on Combining Load Balancers in Azure relevant for your use case
We have 2 servers hosting a particular service on google cloud. How to do a simple round-robin DNS configuration to distribute the load?
According to this thread Google Cloud DNS does not support round-robin.
You can set up DNS round robin with Cloud DNS simply by adding more than one IP address to your DNS record.
You might want to look into Google Compute Engine's Load Balancing options. This will allow you to have one IP address that sends traffic to your two servers. This has a few advantages, including that you can configure it to automatically stop sending traffic to an instance if it fails a health check.
I am starting to develop a webservice that will be hosted in the cloud but needs higher availability than typical cloud SLAs provide.
Typical SLAs, e.g. Windows Azure, promise an availability of 99.9%, i.e. up to 43min downtime per month. I am looking for an order of magnitude better availability (<5min down time per month). While I can configure several load balanced database back-ends to resolve that part of the issue I see a bottleneck at the webserver. If the webserver fails, the whole service is unavailable to the customer. What are the options of reducing that risk without introducing another possible single point of failure? I see the following solutions and drawbacks to each:
SRV-record:
I duplicate the whole infrastructure (and take care that the databases are in sync) and add additional SRV records for the domain so that the user tying to access www.example.com will automatically get forwarded to example.cloud1.com or if that one is offline to example.cloud2.com. Googling around it seems that SRV records are not supported by any major browser, is that true?
second A-record:
Add an additional A-record as alternatives. Drawbacks:
a) at my hosting provider I do not see any possibility to add a second A-record but just one... is that normal?
b)if one server of two servers are down I am not sure if the user gets automatically re-directed to the other one or 50% of all users get a 404 or some other error
Any clues for a best-practice would be appreciated
Cheers,
Sebastian
The availability of the instance i.e. SLA when specified by the Cloud Provider means the "Instance's Health is server running in the context of Hypervisor or Fabric Controller". With that said, you need to take an effort and ensure the instance is not failing because of your app / OS / or pretty much anything running inside the instance. There are few things which devops tend to miss and that kind of hit back hard like for instance - forgetting to configure the OS Updates and Patches.
The fundamental axiom with the availability is the redundancy. More redundant your application / infrastructure is more availabile is your app.
I recommend your to look into the Azure Traffic Manager and then re-work on your architecture. You need not worry about the SRV record or A-Record. Just a CNAME for the traffic manager would do the trick.
The idea of traffic manager is simple, you can tell the traffic
manager to stand after the domain name ( domain name resolution of the
app ) then the traffic manager decides where to send the request on
considerations of factors like Round-Robin, Disaster Management etc.
With the combination of the Traffic Manager and multi-region infrastructure setup; you will march towards the high availability goal.
Links
Azure Traffic Manager Overview
Cloud Power: How to scale Azure Websites globally with Traffic Manager
Maybe You should configure a corosync cluster with DRBD ?
DRBD will ensure You that the data on both nodes are replicated (for example website files and db files).
Apache as web server will be available under a virtual IP to which domain is pointed. In case of one server is down corosync will move all services to second server within few seconds.