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Displaying posts with tag: resilience (reset)

Server Ownership Legalities
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As I reported via Twitter late last week, we encountered an issue that got some of our mail delivery delayed by about a day and a half. I’ll explain more about what happened as I believe in openness on these matters, and also the experience has educational content for others.

Our mail server doesn’t have direct external interaction, it’s shielded by two relays that handle both the inbound MX and the outbound queue. This setup works remarkably well in terms of exposure to spam and other malicious activity. As previously discussed, it appears that it’s more difficult to make mail server infra more resilient without expending lots more time/effort and infrastructure expenditure. Just because of the way the common tools for mail delivery and imap are built, having two or more of each in a semi-active setup gets quite complex. Complexity is in itself a risk so it has to

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Today’s up-time requirements
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When asking about up-time requirements set down in SLAs (Service Level Agreements) with our clients’ clients, we’d hear anything ranging from hours to the familiar five nines, but these days also simply 100% and otherwise penalties apply. From my perspective, there’s not much difference between five nines and 100%, 99.999% uptime over a year amounts to a maximum of little over 5 minutes outage. In many cases, this includes scheduled outages!

So, we can just not have any outages, scheduled or otherwise. Emergency support is not going to help here, because however fast and good they are, you’re already in serious penalty time or well on your way to not having a business any more. Most will respond within say 30 minutes but then need up to a few hours to resolve the issue. That won’t help you, really, will it? And in any case, how are you going to do your

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Quest for Resilience: Multi-DC Masters
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This is a Request for Input. Dual MySQL masters with MMM in a single datacentre are in common use, and other setups like DRBD and of course VM/SAN based failover solutions are conceptually straightforward also. Thus, achieving various forms of resilience within a single data-centre is doable and not costly.

Doing the same across multiple (let’s for simplicity sake limit it to two) datacentres is another matter. MySQL replication works well across longer links, and it can use MySQL’s in-built SSL or tools like stunnel. Of course it needs to be kept an eye on, as usual, but since it’s asynchronous the latency between the datacentres is not a big issue (apart from the fact that the second server gets up-to-date a little bit later).

But as those who have tried will know, having a client (application server) connection to a MySQL instance in a remote data-centre

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Dogfood: making our systems more resilient
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This is a “dogfood” type story (see below for explanation of the term)… Open Query has ideas on resilient architecture which it teaches (training) and recommends (consulting, support) to clients and the general public (blog, conferences, user group talks). Like many other businesses, when we first started we set up our infrastructure quickly and on the cheap, and it’s grown since. That’s how things grow naturally, and is as always a trade-off between keeping your business running and developing while also improving infrastructure (business processes and technical).

Quite a few months ago we also started investing (mostly time) in the technical infrastructure, and slowly moving the various systems across to new servers and splitting things up along the way. Around the same time, the main webserver frequently became unresponsive. I’ll spare

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Continuity of power
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Last night my residential area lost power for about 2 hours, between 2-4 am. This reminded me of something, and there’s analogies to MySQL infrastructure. Power companies have over recent years invested a lot of money in making the supply more reliable. But, it does fail occasionally still.

From my perspective, the question becomes: is it worth the additional investment for the power companies? Those extra few decimal points in reliability come at a very high cost, and still things can go wrong. So a household (or business) that relies on continuity has to put other measures in place anyway. If the power company has an obligation to deliver to certain standards, it might be more economical for them to provide suitable equipment (UPS, small generator) to these households and business (for free!) and the resulting setup would provide actual continuity rather than merely higher

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Showing entries 1 to 5

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