**Affected version:** 7.12 - 7.17.7, 8.0-8.5
**Fixed in:** 7.17.7, 8.5.0

### Problem Description

A continuous transform can fail if a transform is searching at the same time as an ILM action occurs or in general anything that closes an index. This should not happen if transform is configured with a wildcard pattern for the source index, e.g. `filebeat-*`.

In a specific case an ILM policy temporarily closes the index due to the unfollow-the-follower action.

A typical log entry for this bugs contains something like this:

```
task encountered irrecoverable failure: org.elasticsearch.cluster.block.ClusterBlockException: index [ ... ] blocked by: [FORBIDDEN/4/index closed];
```

### Mitigation

A: Restart the transform. This can be automated by monitoring `_stats` and restarting the transform using `_stop?force=true` followed by `_start`.

B: Don't use the ILM unfollow action until a fix is available.

C: **Unreleased**: Starting with 8.5 set the transform to `unattended` mode via `settings`, this will let transform retry even for this failure class

### Solution

If the source of a transform is configured with a wildcard, transform should not treat an index closed exception as an irrecoverable failure.

### Backport

The fix needs to be backported to the `7.17` series.
x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformFailureHandler.java
* @param numFailureRetries the number of configured retries
     */
    private void handleElasticsearchException(ElasticsearchException elasticsearchException, boolean unattended, int numFailureRetries) {
        if (unattended == false && ExceptionRootCauseFinder.IRRECOVERABLE_REST_STATUSES.contains(elasticsearchException.status())) {
            String message = "task encountered irrecoverable failure: " + elasticsearchException.getDetailedMessage();
            fail(message);
        } else {
            retry(elasticsearchException, elasticsearchException.getDetailedMessage(), unattended, numFailureRetries);
        }
    }
    /**
     * Handle a generic illegal argument exception. This is error is irrecoverable.
     * <p>
     * If this exception is caught it is likely a bug somewhere.
     *
     * @param illegalArgumentException IllegalArgumentException thrown
     * @param unattended whether the transform runs in unattended mode
     */
    private void handleIllegalArgumentException(IllegalArgumentException illegalArgumentException, boolean unattended) {
        if (unattended) {
            retry(illegalArgumentException, illegalArgumentException.getMessage(), true, -1);
        } else {
            String message = "task encountered irrecoverable failure: " + illegalArgumentException.getMessage();
            fail(message);
        }
    }
    /**
     * Terminate failure handling with a retry.
     * <p>
     * In case the number of retries are exhausted - and the transform does not run as unattended - the transform