Template

A Template declares the image a steward’s sandbox is made from. A profile’s template names it by its name. Without one the steward starts from E2B’s base template, so a project declares its own when its Ops need tools that base lacks, or to pin the Node the steward runs.

import { Template } from "@intentius/chant-lexicon-e2b";

const steward = new Template({
  name: "chant-steward",
  fromImage: "node:22-bookworm",
  run: ["apt-get update && apt-get install -y --no-install-recommends jq gh && rm -rf /var/lib/apt/lists/*"],
  cpuCount: 2,
  memoryMB: 2048,
});

export { steward };

Properties

Property	Type	Meaning
name	string, required	The template’s name on E2B: lowercase letters, digits, dashes and underscores. A profile’s template names it.
fromImage	string, required	The image the template starts from. Pin a tag.
run	string[]	Shell commands run in order while the template builds, one RUN line each.
env	Record<string, string>	Environment variables set in every sandbox made from the template.
workdir	string	The working directory for the run steps and the start command.
startCmd	string	The start command, passed as --cmd. E2B runs it when the template is snapshotted, so a sandbox starts with it running.
readyCmd	string	The ready command, passed as --ready-cmd. E2B polls it until it exits 0 before it snapshots the template.
cpuCount	number	vCPUs per sandbox. E2B’s default is 2.
memoryMB	number	Memory per sandbox in MiB, an even number. E2B’s default is 1024.

Building it

chant build writes each template as e2b.<name>.Dockerfile beside its output. The JSON index it writes as the main output gives each template a build field, the e2b template create command line that builds it from that Dockerfile. chant does not run it. Run it in the output directory once, and again when the declaration changes:

chant build src --lexicon e2b -o dist/e2b.json
cd dist && e2b template create chant-steward --dockerfile e2b.chant-steward.Dockerfile --cpu-count 2 --memory-mb 2048

A steward that already exists keeps the sandbox it was made with. To move it onto a rebuilt template, delete its sandbox; the next run makes a new one and clones the repository again.

Checks

Id	Severity	When	What it catches
E2B001	error	lint	A cpuCount that is not a whole number of at least 1, or a memoryMB that is not a positive even number. e2b template create refuses an odd memory size.
E2B002	warning	lint	A fromImage with no tag, or on latest. Two builds of the same declaration could then carry different Node or git versions.
E2B011	error	build	A name E2B refuses, or two templates with the same name, whose files would overwrite each other.
E2B012	warning	build	No sign of git or Node: the image is not a full node image (not -slim or -alpine) and no run step installs them. The runtime stops a run at once on a sandbox without either.

E2B012 only sees the declaration. A template from an image that already has both tools can say so with a step such as git --version && node --version.