Fan out isolated batch jobs - Microsandbox

Use one sandbox per independent input when a parser, converter, or other worker should not share a filesystem with its siblings. The host only needs a small loop; the workload stays inside each microVM.

Run a batch

<Steps> <Step title="Create a few inputs"> <CodeGroup> ```sh macOS & Linux mkdir -p jobs results printf '%s\n' '{"id":"alpha","values":[10,20,30]}' > jobs/alpha.json printf '%s\n' '{"id":"beta","values":[7,8,9]}' > jobs/beta.json printf '%s\n' '{"id":"gamma","values":[100,200]}' > jobs/gamma.json ```

powershell

New-Item -ItemType Directory -Force jobs, results | Out-Null
[IO.File]::WriteAllText((Join-Path $PWD 'jobs/alpha.json'), '{"id":"alpha","values":[10,20,30]}')
[IO.File]::WriteAllText((Join-Path $PWD 'jobs/beta.json'), '{"id":"beta","values":[7,8,9]}')
[IO.File]::WriteAllText((Join-Path $PWD 'jobs/gamma.json'), '{"id":"gamma","values":[100,200]}')

</CodeGroup> </Step> <Step title="Run them in parallel">

<Tooltip tip="These jobs work on microsandbox cloud after omitting replace-on-create from the command."><span className="msb-badge-limited">Limited on cloud <Icon icon="circle-info" size={11} /></span></Tooltip>

<CodeGroup> ```bash macOS & Linux pids=() batch_status=0

for input in jobs/*.json; do job="$(basename "$input" .json)" msb run --quiet --name "batch-$job" --replace
--cpus 1 --memory 256M --max-duration 30s
--copy-file "$input:/job/input.json" --workdir /job
--no-net --security restricted
python:3.13.14-alpine3.23 -- python -c
'import json; p=json.load(open("input.json")); print(json.dumps({"id":p["id"],"total":sum(p["values"])}))'
> "results/$job.json" & pids+=("$!") done

for pid in "${pids[@]}"; do wait "$pid" || batch_status=1 done

test "$batch_status" -eq 0


```powershell Windows
$workers = Get-ChildItem jobs/*.json | ForEach-Object {
  $inputPath = $_.FullName
  $jobName = $_.BaseName
  $resultPath = Join-Path $PWD "results/$jobName.json"

  Start-Job -ArgumentList $inputPath, $jobName, $resultPath -ScriptBlock {
    param($inputPath, $jobName, $resultPath)

    $result = & msb run --quiet --name "batch-$jobName" --replace `
      --cpus 1 --memory 256M --max-duration 30s `
      --copy-file "${inputPath}:/job/input.json" --workdir /job `
      --no-net --security restricted `
      python:3.13.14-alpine3.23 -- python -c `
        'import json; p=json.load(open("input.json")); print(json.dumps({"id":p["id"],"total":sum(p["values"])}))'

    $status = $LASTEXITCODE
    [IO.File]::WriteAllText($resultPath, ($result -join [Environment]::NewLine))
    if ($status -ne 0) { throw "batch-$jobName failed" }
  }
}

$workers | Wait-Job | Receive-Job
if ($workers.State -contains 'Failed') { throw 'one or more batch jobs failed' }
$workers | Remove-Job

</CodeGroup>

& provides the concurrency and wait carries worker failures back to the host. CPU, memory, network, and lifetime are bounded independently for every input.

Inspect the results:

<CodeGroup> ```sh macOS & Linux jq . results/*.json ```

powershell

Get-ChildItem results/*.json | ForEach-Object { jq . $_.FullName }

</CodeGroup>

Replace the short Python expression with your worker command. For larger outputs, write to /var/tmp in the guest and use msb cp after the sandbox stops instead of capturing stdout.

</Step> <Step title="Clean up"> <CodeGroup> ```sh macOS & Linux for input in jobs/*.json; do msb rm -f "batch-$(basename "$input" .json)" done ```

powershell

Get-ChildItem jobs/*.json | ForEach-Object {
  msb rm -f "batch-$($_.BaseName)"
}

</CodeGroup>

This loop limits one batch only. Put a queue or global concurrency limit in front of it when several batches can run on the same host.

</Step> </Steps>