# Does experimental feature \`consistent-topology-changes\` support online modification?

**URL:** <https://forum.scylladb.com/t/does-experimental-feature-consistent-topology-changes-support-online-modification/1200>\
**Category:** ScyllaDB\
**Tags:** experimental\
**Created:** [January 16, 2024, 6:31am UTC](https://forum.scylladb.com/t/does-experimental-feature-consistent-topology-changes-support-online-modification/1200 "2024-01-16T06:31:05Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![bo\_li](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.scylladb.com/bo_li/32/438_2.png) [@bo\_li](https://forum.scylladb.com/u/bo_li)\
**Post date:** [January 16, 2024, 6:31am UTC](https://forum.scylladb.com/t/does-experimental-feature-consistent-topology-changes-support-online-modification/1200/1 "2024-01-16T06:31:05Z")

</div>

Now I have a up and normal 5.4.0 cluster.

 ![image](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/1X/b82d9804b3dc5beef45be5d5015b87be8bfc4cf3.png)  
After adding configuration `consistent-topology-changes` to them, only the seed node is functioning properly. The other two nodes are not displayed in the cluster, but their logs do not report any errors.  
 ![image](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/1X/6320e5eb02c0a3ccdee9488d728030c0586201df.png)  
However, the logs of the seed node show that the other two nodes are up and normal.

```auto
INFO 2024-01-16 06:17:27,366 [shard 0:main] raft_group0 - gaining leadership
INFO 2024-01-16 06:17:28,302 [shard 0:goss] gossip - InetAddress 100.71.8.19 is now UP, status = NORMAL
INFO 2024-01-16 06:17:28,328 [shard 0:goss] gossip - InetAddress 100.71.8.18 is now UP, status = NORMAL
INFO 2024-01-16 06:17:28,495 [shard 0:comp] compaction - [Compact system_distributed.cdc_generation_timestamps ebc9ab00-b436-11ee-9ea8-adab234ee8bf] Compacted 2 sstables to [/var/lib/scylla/data/system_distributed/cdc_generation_timestamps-fdf455c4cfec3e009719d7a45436c89d/me-3gct_0hh3_1f0f42euxqvtiwkmv3-big-Data.db:level=0]. 11kB to 5kB (~50% of original) in 1137ms = 9kB/s. ~256 total partitions merged to 1.

```

---

<div class="post-metadata">

**Author:** ![kbr](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.scylladb.com/kbr/32/309_2.png) [@kbr](https://forum.scylladb.com/u/kbr)\
**Post date:** [January 16, 2024, 9:26am UTC](https://forum.scylladb.com/t/does-experimental-feature-consistent-topology-changes-support-online-modification/1200/2 "2024-01-16T09:26:28Z")

</div>

Hi,

The consistent-topology-changes experimental feature does not yet support upgrades. I.e. if you start with a cluster without the feature, and then try to enable it, the cluster will end up in some undefined state.

To get a functioning cluster with consistent-topology-changes, you need to bootstrap it from scratch with this option.

But remember that this is an experimental feature, it’s not production ready. It’s under heavy development with backward incompatible changes happening every week. It’s fine to play with it with clusters that you’re going to discard.