Lelantos: Instant, Isolated Computers on Demand

Overview

Custom templates let you define your own sandbox environment from a Dockerfile. You can install any packages, configure runtimes, set up tools, and specify resource allocation. The build process is asynchronous -- you submit the Dockerfile and poll for build completion.

Creating a Custom Template

const template = await client.createTemplate({
  dockerfile: `
FROM python:3.12-slim
RUN pip install numpy pandas scikit-learn matplotlib
`,
  alias: "data-science",
  cpuCount: 4,
  memoryMB: 2048,
});

console.log("Template ID:", template.templateID);
console.log("Build ID:", template.buildID);

curl -X POST https://api.lelantos.ai/templates \
  -H "X-API-Key: lel_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "dockerfile": "FROM python:3.12-slim\nRUN pip install numpy pandas scikit-learn matplotlib",
    "alias": "data-science",
    "cpuCount": 4,
    "memoryMB": 2048
  }'

Template Configuration

Parameter	Type	Default	Range	Description
`dockerfile`	`string`	(required)	--	Dockerfile content as a string.
`alias`	`string`	(optional)	--	Human-readable name for the template.
`cpuCount`	`number`	2	1 - 8	Number of vCPUs for sandboxes created from this template.
`memoryMB`	`number`	512	128 - 8192	Memory in MB for sandboxes created from this template.

Checking Build Status

Template builds are asynchronous. Poll the build status to know when the template is ready:

const status = await client.getTemplateBuildStatus(
  template.templateID,
  template.buildID,
);

console.log("Status:", status.status);
// "building" | "ready" | "error"

if (status.status === "error") {
  console.error("Build failed:", status.error);
}

curl "https://api.lelantos.ai/templates/TEMPLATE_ID/builds/BUILD_ID" \
  -H "X-API-Key: lel_your_key_here"

Build Status Values

Status	Description
`building`	Template is currently being built.
`ready`	Build completed successfully. Template is ready to use.
`error`	Build failed. Check the error message for details.

Polling Example

async function waitForBuild(client, templateID, buildID) {
  while (true) {
    const status = await client.getTemplateBuildStatus(templateID, buildID);

    if (status.status === "ready") {
      console.log("Template is ready!");
      return;
    }

    if (status.status === "error") {
      throw new Error(`Build failed: ${status.error}`);
    }

    // Wait 2 seconds before checking again
    await new Promise((r) => setTimeout(r, 2000));
  }
}

await waitForBuild(client, template.templateID, template.buildID);

// Now create a sandbox from the template
const sandbox = await client.createSandbox({
  templateID: template.templateID,
});

DNS

Do not add RUN echo "nameserver 8.8.8.8" > /etc/resolv.conf to your Dockerfile. Older versions of this guide recommended it as a workaround, but Docker BuildKit mounts /etc/resolv.conf read-only during builds and the line now fails with Read-only file system. DNS works without it — apt-get, pip install, npm install, etc. resolve normally during the build. If you copied an older template that includes this line, just remove it before rebuilding.

Rebuilding a Template

To update an existing template, create a new template with the same alias. The new build will produce a new template ID. Existing sandboxes running on the old template are not affected.

const updated = await client.createTemplate({
  dockerfile: `
FROM python:3.12-slim
RUN pip install numpy pandas scikit-learn matplotlib seaborn
`,
  alias: "data-science",
  cpuCount: 4,
  memoryMB: 4096, // Increased memory
});

Deleting a Template

Remove a template when it is no longer needed:

await client.deleteTemplate(template.templateID);

curl -X DELETE "https://api.lelantos.ai/templates/TEMPLATE_ID" \
  -H "X-API-Key: lel_your_key_here"

Deleting a template does not affect running sandboxes that were created from it. They will continue to run until they are killed or their timeout expires.

Custom Templates