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Showing posts from October, 2021

EC2 swap device management & fixing "swapoff failed: Cannot allocate memory"

 One of the sillier things I've done as an AWS/linux admin is provision an EBS disk as swap to an EC2 instance. I kept getting max allocate errors for a script I needed to run to execute a series of database queries. Reprovisioning to a new EC2 instance class with more RAM wasn't feasible at the time for some long-forgotten reason.  I would never do this if I owned the disks - provisioning swap to SSD will greatly reduce the lifetime of the disk, among many reasons why this is less than ideal. But Amazon has plenty of money. I figured I could cheaply provision an EBS volume & buy myself enough swap to complete the query. Then, in some point in the future, I could create a more beautimous solution. Well, if you're a sysadmin you know how this story ends. I moved onto other fires/projects, quickly forgot about the swap situation, and here I am years later, deprovisioning the server, in all its swappy glory. This wouldn't warrant a blog post, except for the fact that I

S3 static webhosting, DKIM signature size errors & why DNS prefers UDP

This weekend I spent some time migrating a few low-traffic websites from Nginx to AWS S3's static web hosting service. In theory, this is a straightforward process: move content from the old webroot to an S3 bucket that shares the name of the domain, enable static web hosting for the bucket & set a security policy that enables anonymous web users to see that content. In practice, there's a bit more involved: 1. S3 bucket resource paths can change, which will result in DNS failures unless you use a Route 53 hosted zone. You don't need to buy a domain from Amazon to do this, but you do need to use their nameservers. This isn't free, and there is an extra fee for DNSSEC. 2. Want an SSL/TLS certificate? Of course you do. This means generating a certificate within Amazon Certificate Manager. In most circumstances (without "legacy" client support for example), there is no charge for the certificate. But to serve traffic using that certificate requires provisioni