**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
retry(scriptException, message, true, -1);
        } else {
            fail(message);
        }
    }
    /**
     * Handle bulk indexing exception case. This is error can be irrecoverable.
     *
     * @param bulkIndexingException BulkIndexingException thrown
     * @param unattended whether the transform runs in unattended mode
     * @param numFailureRetries the number of configured retries
     */
    private void handleBulkIndexingException(BulkIndexingException bulkIndexingException, boolean unattended, int numFailureRetries) {
        if (unattended == false && bulkIndexingException.isIrrecoverable()) {
            String message = TransformMessages.getMessage(
                TransformMessages.LOG_TRANSFORM_PIVOT_IRRECOVERABLE_BULK_INDEXING_ERROR,
                bulkIndexingException.getDetailedMessage()
            );
            fail(message);
        } else {
            retry(bulkIndexingException, bulkIndexingException.getDetailedMessage(), unattended, numFailureRetries);
        }
    }
    /**
     * Handle a generic elasticsearch exception. This is error can be irrecoverable.
     * <p>
     * The failure is classified using the http status code from the exception.
     *
     * @param elasticsearchException ElasticsearchException thrown
     * @param unattended whether the transform runs in unattended mode