A Plain-English Glossary of Cloud Infrastructure Terms
Short, practical definitions of the terms that appear constantly in provider consoles and account listings, with the distinctions that actually matter.
Cloud vocabulary is inconsistent between providers, and the same word occasionally means different things. These are working definitions, written for the sense in which the terms are actually used.
Compute
vCPU. A virtual processor presented to a guest. Usually a hardware thread rather than a whole physical core. Comparable within one provider and family, not across them. See what vCPU counts mean.
Instance. A running virtual machine, usually implying something replaceable.
Droplet. DigitalOcean’s name for a virtual machine.
Image. A template a machine is created from. Contains the operating system and anything baked in.
Snapshot. A point-in-time copy of a disk, used to restore or to clone.
Placement
Region. A geographic area of data centres. Largely independent of other regions.
Availability zone. An isolated failure domain within a region, linked to its siblings by low-latency networking.
Data residency. A requirement that data remain in a particular jurisdiction. Decided by placement.
Storage
Block storage. A virtual disk attached to one machine, formatted with a filesystem.
Object storage. Storage addressed by key over HTTP, suited to large numbers of files accessed by many clients.
IOPS. Input/output operations per second, a measure of how many separate reads and writes storage can serve.
Networking
Egress. Data leaving the provider’s network. Usually the most expensive direction of transfer.
Elastic or floating IP. An address you reserve and can move between machines.
Security group or firewall. Rules controlling which traffic reaches a machine.
Port 25. The port used for server-to-server mail delivery, restricted by default on most providers. See port 25 and outbound mail.
Accounts and access
IAM. Identity and access management: the system of users, roles and policies controlling who may do what.
Root user. The original account identity with unrestricted authority. Should be secured and then left alone.
Service account. A non-human identity used by applications.
Quota. A ceiling on how much of a resource an account may consume, usually per region.
Billing
On-demand. Pay for what you use, no commitment, highest unit price.
Committed use. A discount in exchange for a usage promise over a term.
Promotional credit. A provider-granted balance offsetting eligible charges, usually dated and service-restricted.
Upgraded. A verified billing relationship without trial ceilings. See what upgraded means.
Cloud accounts on OldCloudShop
Ten providers, every configuration and the starting price for each.
Continue in the library
Other entries covering account structure, billing, security and provider infrastructure.