Lab preparation is slow or fails

When you start a lab, Klastro creates a real, isolated environment for you. While it is being prepared, the lab shows Preparing your environment and the current stage:

Message	What is happening
Reserving your environment…	Your environment is being reserved.
Starting the machines…	The machines or the cluster are booting.
Waiting for your session to be authorized…	The lab waits for someone to approve it (see below).
Setting up your lab… with 2 of 5 steps done	The scenario’s setup steps are running, one by one. The list shows each step.
Starting up…	The last moments before the terminal opens.

Each problem below is laid out as Symptom, Cause and Fix.

Preparation takes a long time

Symptom. The lab stays on Preparing your environment for several minutes.

Cause. Preparation time depends on the scenario. A single cluster is usually ready quickly; a scenario with several machines and a long list of setup steps (installing a cluster from scratch, deploying tools) takes noticeably longer.

Fix. Wait as long as the step counter keeps moving: the screen shows real progress, not an estimate. Do not reload repeatedly or start the lab again from the catalog. If the counter has not moved for a long time, report a problem from the lab: the setup progress is attached to your report.

“One step did not complete. We are retrying it”

Symptom. The preparation screen shows One step did not complete. We are retrying it — this may take a little longer.

Cause. A setup step failed, often because something it depends on was not ready yet. Klastro retries it automatically.

Fix. Wait. Most retries succeed. If the message stays and the counter stops moving, report the problem from the lab.

“Waiting for your session to be authorized…”

Symptom. The lab waits on Waiting for your session to be authorized… (or Waiting for authorization… in the terminal).

Cause. The assessment is set to manual approval: a recruiter must authorize your session before it starts.

Fix. Keep the page open. The lab continues on its own once the recruiter approves. If nothing happens, contact the recruiter who invited you.

“The lab session encountered an error”

Symptom. The lab page shows The lab session encountered an error.

Cause. The page could not load the session, or the environment could not be created.

Fix. Reload the page once. If the error comes back, go to My Sessions, check the session’s status, and report a problem or open a ticket with the session id.

The lab does not start at all

Message	Cause	Fix
You’re at your session limit	Your plan runs a set number of sessions at once.	Pause or End one of the sessions listed, then Try again. See Manage your sessions.
Too many sessions are running right now…	The platform or your organization has reached its number of labs running at once.	Wait a few minutes and try again. Paused labs do not count.
A message starting with ERR_INSUFFICIENT_CREDITS	Your balance does not cover one hour of this environment.	See Credits and paused labs.
Upgrade to launch instead of a start button	Your plan does not include this kind of lab.	See Plans and credits.
Session did not start. Please try again.	A temporary problem.	Try again. If it persists, open a ticket.

The lab ended on its own

Symptom. You receive the notification Your lab has ended (“… reached its time limit and was shut down.”), or the lab shows This environment has ended.

Cause. Every lab has a maximum lifetime set by the scenario. When it is reached, the environment is stopped. Checks you had already passed are kept.

Fix. Start the scenario again from the catalog if you want to continue practising. To keep an environment between work sessions, pause it before you leave rather than leaving it running.