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Questions tagged [failover]

In computing, failover is automatic switching to a redundant or standby computer server, system, or network upon the failure or abnormal termination of the previously active application, server, system, or network. Failover and switchover are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention.

In computing, failover is automatic switching to a redundant or standby computer server, system, or network upon the failure or abnormal termination of the previously active application,server, system, or network. Failover and switchover are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention.

Systems designers usually provide failover capability in servers, systems or networks requiring continuous availability and a high degree of reliability. At server level, failover automation usually uses a "heartbeat" cable that connects two servers. As long as a regular "pulse" or "heartbeat" continues between the main server and the second server, the second server will not initiate its systems. There may also be a third "spare parts" server that has running spare components for "hot" switching to prevent downtime. The second server takes over the work of the first as soon as it detects an alteration in the "heartbeat" of the first machine. Some systems have the ability to send a notification of failover.

Some systems, intentionally, do not failover entirely automatically, but require human intervention. This "automated with manual approval" configuration runs automatically once a human has approved the failover.

Source: wikipedia

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100% uptime for a web application

We received an interesting "requirement" from a client today. They want 100% uptime with off-site failover on a web application. From our web application's viewpoint, this isn't an issue. It was designed to be able to scale out across multiple…
NotMe
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Why is DNS failover not recommended?

From reading, it seems like DNS failover is not recommended just because DNS wasn't designed for it. But if you have two webservers on different subnets hosting redundant content, what other methods are there to ensure that all traffic gets routed…
Lin
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nginx automatic failover load balancing

I'm using nginx and NginxHttpUpstreamModule for loadbalancing. My config is very simple: upstream lb { server 127.0.0.1:8081; server 127.0.0.1:8082; } server { listen 89; server_name localhost; location / { …
robinmag
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nginx reverse proxy - try upstream A, then B, then A again

I'm trying to set up nginx as a reverse proxy, with a large number of backend servers. I'd like to start up the backends on-demand (on the first request that comes in), so I have a control process (controlled by HTTP requests) which starts up the…
Vladimir Panteleev
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Cheapest iSCSI SAN for Windows 2008/SQL Server clustering?

Are there any production-quality iSCSI SANs suitable for use with Windows Server 2008/SQL Server for failover clustering? So far, I've only seen Dell's MD3000i, and HP's MSA 2000 (2012i), which both are around $6K with a minimal disk configuration.…
MichaelGG
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LVS vs HAProxy, which should I choose?

I am looking for a solution to load balancing and failover strategy, mainly for big web applications. We have many services to be balanced, such as web, MySQL, and many other HTTP or TCP based services. But I am not sure what their pros and cons…
Mickey Shine
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nginx failover without load balancing

I'm having trouble configuring nginx. I'm using nignx as a reverse proxy. I want to send my all requests to my first server. If the first server is down, I want to send requests to second server. In short, how can I have a failover solution without…
Serhat
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DNS Round Robin: Do browsers stick to one IP as long as it is online?

How do most browsers behave if they get multiple A-records from the DNS server? Do the stick to one IP as long as it is reachable (and only use another if the IP is down)? Or do they switch all the time for no reason? If the majority current…
HiPerFreak
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Multi-site high availability

We have a SaaS application that we need to be highly available. We already have an expensive, well-maintained Hyper-V failover cluster, but today the datacenter where we host that cluster had a five-hour power outage that knocked us completely…
Mike
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How to setup HAProxy with failover?

I understand that, to get failover on an HAProxy load balancing setup, you need two machines running HAproxy (and route it to several webserver instances). But in this case, say abcd.com, how do we split/route this traffic to 2 IP addresses instead…
mixdev
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What happens when a load balancer fails?

Let's say I'm using Amazon's EC2 load balancer. I have it hooked up to two instances (excuse me if my terminology isn't correct). What happens if the load balancer fails? Do both instances fail to work now?
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When my A web server gets unplugged, how do I automatically redirect all the users to my B web server in another city, and vice versa?

When my A web server gets unplugged, how do I automatically redirect all the users to my B web server in another city, and vice versa? A load-balancing switch does what I want, except I can't figure out how to get it to work unless both web servers…
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How do you automate failover on EC2?

Of the folks managing their own clusters (i.e. not using/paying for Amazon Autoscale, Rightscale, Scalr, etc.), how are you managing your instances on EC2 and handling (e.g.) failover? I'm wondering if most folks just end up writing their own…
Yang
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nginx use proxy cache if backend is down

I need to nginx proxy use cache if backend server down: this is my configuration. but seems be nginx use cache without check backend server. http { # ... proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; …
sweb
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How browsers handle multiple IPs

Can someone direct me to information on exact browsers behavior when browser gets multiple A records for a given hostname (say ip1 and ip2), and one of them is not accessible. I interested in EXACT details, like (but not limited to): Will browser…
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