# Revisions and Rollback
source: https://docs.chalk.ai/docs/scaling-groups/revisions-and-rollback

## Roll a new revision onto a scaling group, list its revisions, and roll back to an earlier one.

Each deploy of a scaling group records an immutable revision of the group's spec. The group keeps
the same ID, name, and web_url across revisions, and serves one revision at a
time.

Redeploying with the same name from ScalingGroup(...).deploy() or
chalk scaling-group create records a new revision and routes all traffic to
it. That is how you roll a new image or spec onto a running group. To record a
new revision from the CLI without serving it, add --no-traffic. The group
keeps serving its current revision until you select the new one.

To roll back, select an earlier revision. Selecting a revision routes all
traffic to it and does not record a new revision. Revision history is also on
the scaling group's Revisions tab in the dashboard.

### From the SDK

This example uses the app.py file from the
Quick start, saved in the same directory. It
deploys two revisions of a group, lists them, and rolls back to the first:

```
import chalkcompute

img = (
    chalkcompute.Image.debian_slim("3.12")
    .pip_install(["flask"])
    .add_local_file("./app.py", "/app/app.py")
    .entrypoint(["python", "/app/app.py"])
)

sg = chalkcompute.ScalingGroup(
    image=img,
    name="hello-api",
    port=8080,
    env={"APP_VERSION": "1"},
).deploy()

# Deploying again under the same name records a second revision.
sg = chalkcompute.ScalingGroup(
    image=img,
    name="hello-api",
    port=8080,
    env={"APP_VERSION": "2"},
).deploy()

revisions = sg.revisions()
for rev in revisions:
    print(rev.id, rev.status, rev.is_current)

sg.rollback(revisions[1].id)
print(sg.refresh().current_revision_id)
```

revisions() returns the group's revisions, newest first. The serving revision
has is_current set to True, and the others report the Superseded status.
rollback(revision_id) selects that revision and waits until the group is
ready. Pass wait_ready=False to return without waiting, or timeout to change
the wait from its default of 300 seconds.

### From the CLI

List a group's revisions, inspect one, and route traffic to it:

```
$ chalk scaling-group revisions list --name=hello-api
$ chalk scaling-group revisions get --name=hello-api --revision-id=<revision-id>
$ chalk scaling-group update-traffic --name=hello-api --revision-id=<revision-id>
```

update-traffic routes all of the group's traffic to the revision you name.
Use it to roll back, or to start serving a revision you recorded with
--no-traffic. Each command also accepts --id in place of --name.