[discrete]
[[breaking_80_cluster_node_setting_changes]]
==== Cluster and node setting changes

//NOTE: The notable-breaking-changes tagged regions are re-used in the
//Installation and Upgrade Guide

//tag::notable-breaking-changes[]
TIP: {ess-setting-change}

.`action.destructive_requires_name` now defaults to `false`. {ess-icon}
[%collapsible]
====
*Details* +
The default for the `action.destructive_requires_name` setting changes from `false`
to `true` in {es} 8.0.0.

Previously, defaulting to `false` allowed users to use wildcard
patterns to delete, close, or change index blocks on indices. 
To prevent the accidental deletion of indices that happen to match a
wildcard pattern, we now default to requiring that destructive
operations explicitly name the indices to be modified.

*Impact* +
To use wildcard patterns for destructive actions, set
`action.destructive_requires_name` to `false` using the
{ref}/cluster-update-settings.html[] cluster settings API].
====

.You can no longer set `xpack.searchable.snapshot.shared_cache.size` on non-frozen nodes.
[%collapsible]
====
*Details* +
You can no longer set
{ref}/searchable-snapshots.html#searchable-snapshots-shared-cache[`xpack.searchable.snapshot.shared_cache.size`]
on a node that doesn't have the `data_frozen` node role. This setting reserves
disk space for the shared cache of partially mounted indices. {es} only
allocates partially mounted indices to nodes with the `data_frozen` role.

*Impact* +
Remove `xpack.searchable.snapshot.shared_cache.size` from `elasticsearch.yml`
for nodes that don't have the `data_frozen` role. Specifying the setting on a
non-frozen node will result in an error on startup.
====

[[max_clause_count_change]]
.The `indices.query.bool.max_clause_count` setting now limits all query clauses.
[%collapsible]
====
*Details* +
Previously, the `indices.query.bool.max_clause_count` would apply to the number
of clauses of a single `bool` query. It now applies to the total number of
clauses of the rewritten query. To reduce chances of breaks, its
default value has been bumped from 1024 to 4096.

*Impact* +
Queries with many clauses should be avoided whenever possible. 
If you previously bumped this setting to accommodate heavy queries, 
you might need to increase it further. 
====

[[ilm-poll-interval-limit]]
.`indices.lifecycle.poll_interval` must be greater than `1s`.
[%collapsible]
====
*Details* +
Setting `indices.lifecycle.poll_interval` too low can cause
excessive load on a cluster. The poll interval must now be at least `1s` (one second).

*Impact* +
Set `indices.lifecycle.poll_interval` setting to `1s` or
greater in `elasticsearch.yml` or through the
{ref}/cluster-update-settings.html[cluster update settings API].

Setting `indices.lifecycle.poll_interval` to less than `1s` in
`elasticsearch.yml` will result in an error on startup.
{ref}/cluster-update-settings.html[Cluster update settings API] requests that
set `indices.lifecycle.poll_interval` to less than `1s` will return an error.
====

.The file and native realms are now enabled unless explicitly disabled.
[%collapsible]
====
*Details* +
The file and native realms are now enabled unless explicitly disabled. If
explicitly disabled, the file and native realms remain disabled at all times.

Previously, the file and native realms had the following implicit behaviors:

* If the file and native realms were not configured, they were implicitly disabled
if any other realm was configured.

* If no other realm was available because realms were either not configured,
not permitted by license, or explicitly disabled, the file and native realms
were enabled, even if explicitly disabled.

*Impact* +
To explicitly disable the file or native realm, set the respective
`file.<realm-name>.enabled` or `native.<realm-name>.enabled` setting to `false`
under the `xpack.security.authc.realms` namespace in `elasticsearch.yml`.

The following configuration example disables the native realm and the file realm.

[source,yaml]
----
xpack.security.authc.realms:

  native.realm1.enabled: false
  file.realm2.enabled: false

  ...
----
====

.The realm `order` setting is now required.
[%collapsible]
====
*Details* +
The `xpack.security.authc.realms.{type}.{name}.order` setting is now required and must be
specified for each explicitly configured realm. Each value must be unique.

*Impact* +
The cluster will fail to start if the requirements are not met.

For example, the following configuration is invalid:
[source,yaml]
--------------------------------------------------
xpack.security.authc.realms.kerberos.kerb1:
  keytab.path: es.keytab
  remove_realm_name: false
--------------------------------------------------

And must be configured as:
[source,yaml]
--------------------------------------------------
xpack.security.authc.realms.kerberos.kerb1:
  order: 0
  keytab.path: es.keytab
  remove_realm_name: false
--------------------------------------------------
====

[[breaking_80_allocation_change_include_relocations_removed]]
.`cluster.routing.allocation.disk.include_relocations` has been removed.
[%collapsible]
====
*Details* +
{es} now always accounts for the sizes of relocating shards when making
allocation decisions based on the disk usage of the nodes in the cluster. In
earlier versions, you could disable this by setting `cluster.routing.allocation.disk.include_relocations` to `false`.
That could result in poor allocation decisions that could overshoot watermarks and require significant
extra work to correct. The `cluster.routing.allocation.disk.include_relocations` setting has been removed.

*Impact* +
Remove the `cluster.routing.allocation.disk.include_relocations`
setting. Specifying this setting in `elasticsearch.yml` will result in an error
on startup.
====

.cluster.join.timeout` has been removed.
[%collapsible]
====
*Details* +
The `cluster.join.timeout` setting has been removed. Join attempts no longer
time out.

*Impact* +
Remove `cluster.join.timeout` from `elasticsearch.yml`.
====

.`discovery.zen` settings have been removed.
[%collapsible]
====
*Details* +
All settings under the `discovery.zen` namespace are no longer supported. They existed only only for BWC reasons in 7.x. This includes:

- `discovery.zen.minimum_master_nodes`
- `discovery.zen.no_master_block`
- `discovery.zen.hosts_provider`
- `discovery.zen.publish_timeout`
- `discovery.zen.commit_timeout`
- `discovery.zen.publish_diff.enable`
- `discovery.zen.ping.unicast.concurrent_connects`
- `discovery.zen.ping.unicast.hosts.resolve_timeout`
- `discovery.zen.ping.unicast.hosts`
- `discovery.zen.ping_timeout`
- `discovery.zen.unsafe_rolling_upgrades_enabled`
- `discovery.zen.fd.connect_on_network_disconnect`
- `discovery.zen.fd.ping_interval`
- `discovery.zen.fd.ping_timeout`
- `discovery.zen.fd.ping_retries`
- `discovery.zen.fd.register_connection_listener`
- `discovery.zen.join_retry_attempts`
- `discovery.zen.join_retry_delay`
- `discovery.zen.join_timeout`
- `discovery.zen.max_pings_from_another_master`
- `discovery.zen.send_leave_request`
- `discovery.zen.master_election.wait_for_joins_timeout`
- `discovery.zen.master_election.ignore_non_master_pings`
- `discovery.zen.publish.max_pending_cluster_states`

*Impact* +
Remove the `discovery.zen` settings from `elasticsearch.yml`. Specifying these settings will result in an error on startup.
====

.`http.content_type.required` has been removed.
[%collapsible]
====
*Details* +
The `http.content_type.required` setting was deprecated in Elasticsearch 6.0
and has been removed in Elasticsearch 8.0. The setting was introduced in
Elasticsearch 5.3 to prepare users for Elasticsearch 6.0, where content type
auto detection was removed for HTTP requests.

*Impact* +
Remove the `http.content_type.required` setting from `elasticsearch.yml`. Specifying this setting  will result in an error on startup.
====

.`http.tcp_no_delay` has been removed.
[%collapsible]
====
*Details* +
The `http.tcp_no_delay` setting was deprecated in 7.x and has been removed in 8.0. Use`http.tcp.no_delay` instead.

*Impact* +
Replace the `http.tcp_no_delay` setting with `http.tcp.no_delay`.  
Specifying  `http.tcp_no_delay` in `elasticsearch.yml` will
result in an error on startup.
====

.`network.tcp.connect_timeout` has been removed.
[%collapsible]
====
*Details* +
The `network.tcp.connect_timeout` setting was deprecated in 7.x and has been removed in 8.0. This setting
was a fallback setting for `transport.connect_timeout`.

*Impact* +
Remove the`network.tcp.connect_timeout` setting. 
Use the `transport.connect_timeout` setting to change the default connection
timeout for client connections. Specifying
`network.tcp.connect_timeout` in `elasticsearch.yml` will result in an
error on startup.
====

.`node.max_local_storage_nodes` has been removed.
[%collapsible]
====
*Details* +
The `node.max_local_storage_nodes` setting was deprecated in 7.x and
has been removed in 8.0. Nodes should be run on separate data paths
to ensure that each node is consistently assigned to the same data path.

*Impact* +
Remove the `node.max_local_storage_nodes` setting. Specifying this
setting in `elasticsearch.yml` will result in an error on startup.
====

[[accept-default-password-removed]]
.The `accept_default_password` setting has been removed.
[%collapsible]
====
*Details* +
The `xpack.security.authc.accept_default_password` setting has not had any affect
since the 6.0 release of {es} and is no longer allowed.

*Impact* +
Remove  the `xpack.security.authc.accept_default_password` setting from `elasticsearch.yml`.
Specifying this setting will result in an error on startup.
====

[[roles-index-cache-removed]]
.The `roles.index.cache.*` settings have been removed.
[%collapsible]
====
*Details* +
The `xpack.security.authz.store.roles.index.cache.max_size` and
`xpack.security.authz.store.roles.index.cache.ttl` settings have
been removed. These settings have been redundant and deprecated
since the 5.2 release of {es}.

*Impact* +
Remove the `xpack.security.authz.store.roles.index.cache.max_size`
and `xpack.security.authz.store.roles.index.cache.ttl` settings from `elasticsearch.yml` . 
Specifying these settings will result in an error on startup.
====

[[separating-node-and-client-traffic]]
.The `transport.profiles.*.xpack.security.type` setting has been removed.
[%collapsible]
====
*Details* +
The `transport.profiles.*.xpack.security.type` setting is no longer supported.
The Transport Client has been removed and all client traffic now uses
the HTTP transport. Transport profiles using this setting should be removed.

*Impact* +
Remove the `transport.profiles.*.xpack.security.type` setting from `elasticsearch.yml`.
Specifying this setting in a transport profile will result in an error on startup.
====

[discrete]
[[saml-realm-nameid-changes]]
.The `nameid_format` SAML realm setting no longer has a default value.
[%collapsible]
====
*Details* +
In SAML, Identity Providers (IdPs) can either be explicitly configured to
release a `NameID` with a specific format, or configured to attempt to conform
with the requirements of a Service Provider (SP). The SP declares its
requirements in the `NameIDPolicy` element of a SAML Authentication Request.
In {es}, the `nameid_format` SAML realm setting controls the `NameIDPolicy`
value.

Previously, the default value for `nameid_format` was
`urn:oasis:names:tc:SAML:2.0:nameid-format:transient`. This setting created
authentication requests that required the IdP to release `NameID` with a
`transient` format.

The default value has been removed, which means that {es} will create SAML Authentication Requests by default that don't put this requirement on the
IdP. If you want to retain the previous behavior, set `nameid_format` to
`urn:oasis:names:tc:SAML:2.0:nameid-format:transient`.

*Impact* +
If you currently don't configure `nameid_format` explicitly, it's possible
that your IdP will reject authentication requests from {es} because the requests
do not specify a `NameID` format (and your IdP is configured to expect one).
This mismatch can result in a broken SAML configuration. If you're unsure whether
your IdP is explicitly configured to use a certain `NameID` format and you want to retain current behavior
, try setting `nameid_format` to `urn:oasis:names:tc:SAML:2.0:nameid-format:transient` explicitly.
====

.The `xpack.security.transport.ssl.enabled` setting is now required to configure `xpack.security.transport.ssl` settings.
[%collapsible]
====
*Details* +
It is now an error to configure any SSL settings for
`xpack.security.transport.ssl` without also configuring
`xpack.security.transport.ssl.enabled`.

*Impact* +
If using other `xpack.security.transport.ssl` settings, you must explicitly
specify the `xpack.security.transport.ssl.enabled` setting.

If you do not want to enable SSL and are currently using other
`xpack.security.transport.ssl` settings, do one of the following:

* Explicitly specify `xpack.security.transport.ssl.enabled` as `false`
* Discontinue use of other `xpack.security.transport.ssl` settings

If you want to enable SSL, follow the instructions in
{ref}/configuring-tls.html#tls-transport[Encrypting communications between nodes
in a cluster]. As part of this configuration, explicitly specify
`xpack.security.transport.ssl.enabled` as `true`.

For example, the following configuration is invalid:
[source,yaml]
--------------------------------------------------
xpack.security.transport.ssl.keystore.path: elastic-certificates.p12
xpack.security.transport.ssl.truststore.path: elastic-certificates.p12
--------------------------------------------------

And must be configured as:
[source,yaml]
--------------------------------------------------
xpack.security.transport.ssl.enabled: true <1>
xpack.security.transport.ssl.keystore.path: elastic-certificates.p12
xpack.security.transport.ssl.truststore.path: elastic-certificates.p12
--------------------------------------------------
<1> or `false`.
====

.The `xpack.security.http.ssl.enabled` setting is now required to configure `xpack.security.http.ssl` settings.
[%collapsible]
====
*Details* +
It is now an error to configure any SSL settings for
`xpack.security.http.ssl` without also configuring
`xpack.security.http.ssl.enabled`.

*Impact* +
If using other `xpack.security.http.ssl` settings, you must explicitly
specify the `xpack.security.http.ssl.enabled` setting.

If you do not want to enable SSL and are currently using other
`xpack.security.http.ssl` settings, do one of the following:

* Explicitly specify `xpack.security.http.ssl.enabled` as `false`
* Discontinue use of other `xpack.security.http.ssl` settings

If you want to enable SSL, follow the instructions in
{ref}/configuring-tls.html#tls-http[Encrypting HTTP client communications]. As part
of this configuration, explicitly specify `xpack.security.http.ssl.enabled`
as `true`.

For example, the following configuration is invalid:
[source,yaml]
--------------------------------------------------
xpack.security.http.ssl.certificate: elasticsearch.crt
xpack.security.http.ssl.key: elasticsearch.key
xpack.security.http.ssl.certificate_authorities: [ "corporate-ca.crt" ]
--------------------------------------------------

And must be configured as either:
[source,yaml]
--------------------------------------------------
xpack.security.http.ssl.enabled: true <1>
xpack.security.http.ssl.certificate: elasticsearch.crt
xpack.security.http.ssl.key: elasticsearch.key
xpack.security.http.ssl.certificate_authorities: [ "corporate-ca.crt" ]
--------------------------------------------------
<1> or `false`.
====

.A `xpack.security.transport.ssl` certificate and key are now required to enable SSL for the transport interface.
[%collapsible]
====
*Details* +
It is now an error to enable SSL for the transport interface without also configuring
a certificate and key through use of the `xpack.security.transport.ssl.keystore.path`
setting or the `xpack.security.transport.ssl.certificate` and
`xpack.security.transport.ssl.key` settings.

*Impact* +
If `xpack.security.transport.ssl.enabled` is set to `true`, provide a
certificate and key using the `xpack.security.transport.ssl.keystore.path`
setting or the `xpack.security.transport.ssl.certificate` and
`xpack.security.transport.ssl.key` settings. If a certificate and key is not
provided, {es} will return in an error on startup.
====

.A `xpack.security.http.ssl` certificate and key are now required to enable SSL for the HTTP server.
[%collapsible]
====
*Details* +
It is now an error to enable SSL for the HTTP (Rest) server without also configuring
a certificate and key through use of the `xpack.security.http.ssl.keystore.path`
setting or the `xpack.security.http.ssl.certificate` and
`xpack.security.http.ssl.key` settings.

*Impact* +
If `xpack.security.http.ssl.enabled` is set to `true`, provide a certificate and
key using the `xpack.security.http.ssl.keystore.path` setting or the
`xpack.security.http.ssl.certificate` and `xpack.security.http.ssl.key`
settings. If certificate and key is not provided, {es} will return in an error
on startup.
====

.PKCS#11 keystores and trustores cannot be configured in `elasticsearch.yml`
[%collapsible]
====
*Details* +
The settings `*.ssl.keystore.type` and `*.ssl.truststore.type` no longer accept "PKCS11" as a valid type.
This applies to all SSL settings in Elasticsearch, including

- `xpack.security.http.keystore.type`
- `xpack.security.transport.keystore.type`
- `xpack.security.http.truststore.type`
- `xpack.security.transport.truststore.type`

As well as SSL settings for security realms, watcher and monitoring.

Use of a PKCS#11 keystore or truststore as the JRE's default store is not affected.

*Impact* +
If you have a PKCS#11 keystore configured within your `elasticsearch.yml` file, you must remove that
configuration and switch to a supported keystore type, or configure your PKCS#11 keystore as the
JRE default store.
====

.The `kibana` user has been replaced by `kibana_system`.
[%collapsible]
====
*Details* +
The `kibana` user was historically used to authenticate {kib} to {es}.
The name of this user was confusing, and was often mistakenly used to login to {kib}.
This has been renamed to `kibana_system` in order to reduce confusion, and to better
align with other built-in system accounts.

*Impact* +
Replace any use of the `kibana` user with the `kibana_system` user. Specifying
the `kibana` user in `kibana.yml` will result in an error on startup.

If your `kibana.yml` used to contain:
[source,yaml]
--------------------------------------------------
elasticsearch.username: kibana
--------------------------------------------------

then you should update to use the new `kibana_system` user instead:
[source,yaml]
--------------------------------------------------
elasticsearch.username: kibana_system
--------------------------------------------------

IMPORTANT: The new `kibana_system` user does not preserve the previous `kibana`
user password. You must explicitly set a password for the `kibana_system` user.
====

[[search-remote-settings-removed]]
.The `search.remote.*` settings have been removed.
[%collapsible]
====
*Details* +
In 6.5 these settings were deprecated in favor of `cluster.remote`. In 7.x we
provided automatic upgrading of these settings to their `cluster.remote`
counterparts. In 8.0.0, these settings have been removed. Elasticsearch will
refuse to start if you have these settings in your configuration or cluster
state.

*Impact* +
Use the replacement `cluster.remote` settings. Discontinue use of the
`search.remote.*` settings. Specifying these settings in `elasticsearch.yml`
will result in an error on startup.
====

[[remove-pidfile]]
.The `pidfile` setting has been replaced by `node.pidfile`.
[%collapsible]
====
*Details* +
To ensure that all settings are in a proper namespace, the `pidfile` setting was
previously deprecated in version 7.4.0 of Elasticsearch, and is removed in
version 8.0.0. Instead, use `node.pidfile`.

*Impact* +
Use the `node.pidfile` setting. Discontinue use of the `pidfile` setting.
Specifying the `pidfile` setting in `elasticsearch.yml` will result in an error
on startup.
====

[[remove-processors]]
.The `processors` setting has been replaced by `node.processors`.
[%collapsible]
====
*Details* +
To ensure that all settings are in a proper namespace, the `processors` setting
was previously deprecated in version 7.4.0 of Elasticsearch, and is removed in
version 8.0.0. Instead, use `node.processors`.

*Impact* +
Use the `node.processors` setting. Discontinue use of the `processors` setting.
Specifying the `processors` setting in `elasticsearch.yml` will result in an
error on startup.
====

.The `node.processors` setting can no longer exceed the available number of processors.
[%collapsible]
====
*Details* +
Previously it was possible to set the number of processors used to set the
default sizes for the thread pools to be more than the number of available
processors. As this leads to more context switches and more threads but without
an increase in the number of physical CPUs on which to schedule these additional
threads, the `node.processors` setting is now bounded by the number of available
processors.

*Impact* +
If specified, ensure the value of `node.processors` setting does not exceed the
number of available processors. Setting the `node.processors` value greater than
the number of available processors in `elasticsearch.yml` will result in an
error on startup.
====

.The `cluster.remote.connect` setting has been removed.
[%collapsible]
====
*Details* +
In Elasticsearch 7.7.0, the setting `cluster.remote.connect` was deprecated in
favor of setting `node.remote_cluster_client`. In Elasticsearch 8.0.0, the
setting `cluster.remote.connect` is removed.

*Impact* +
Use the `node.remote_cluster_client` setting. Discontinue use of the
`cluster.remote.connect` setting. Specifying the `cluster.remote.connect`
setting in `elasticsearch.yml` will result in an error on startup.
====

.The `node.local_storage` setting has been removed.
[%collapsible]
====
*Details* +
In Elasticsearch 7.8.0, the setting `node.local_storage` was deprecated and
beginning in Elasticsearch 8.0.0 all nodes will require local storage. Therefore,
the `node.local_storage` setting has been removed.

*Impact* +
Discontinue use of the `node.local_storage` setting. Specifying this setting in
`elasticsearch.yml` will result in an error on startup.
====

.The `auth.password` setting for HTTP monitoring has been removed.
[%collapsible]
====
*Details* +
In Elasticsearch 7.7.0, the setting `xpack.monitoring.exporters.<exporterName>.auth.password`
was deprecated in favor of setting `xpack.monitoring.exporters.<exporterName>.auth.secure_password`.
In Elasticsearch 8.0.0, the setting `xpack.monitoring.exporters.<exporterName>.auth.password` is
removed.

*Impact* +
Use the `xpack.monitoring.exporters.<exporterName>.auth.secure_password`
setting. Discontinue use of the
`xpack.monitoring.exporters.<exporterName>.auth.password` setting. Specifying
the `xpack.monitoring.exporters.<exporterName>.auth.password` setting in
`elasticsearch.yml` will result in an error on startup.
====

.Settings used to disable basic license features have been removed.
[%collapsible]
====
*Details* +
The following settings were deprecated in {es} 7.8.0 and have been removed
in {es} 8.0.0:

* `xpack.enrich.enabled`
* `xpack.flattened.enabled`
* `xpack.ilm.enabled`
* `xpack.monitoring.enabled`
* `xpack.rollup.enabled`
* `xpack.slm.enabled`
* `xpack.sql.enabled`
* `xpack.transform.enabled`
* `xpack.vectors.enabled`

These basic license features are now always enabled.

If you have disabled ILM so that you can use another tool to manage Watcher
indices, the newly introduced `xpack.watcher.use_ilm_index_management` setting
may be set to false.

*Impact* +
Discontinue use of the removed settings. Specifying these settings in
`elasticsearch.yml` will result in an error on startup.
====

.Settings used to defer cluster recovery pending a certain number of master nodes have been removed.
[%collapsible]
====
*Details* +
The following cluster settings have been removed:

* `gateway.expected_nodes`
* `gateway.expected_master_nodes`
* `gateway.recover_after_nodes`
* `gateway.recover_after_master_nodes`

It is safe to recover the cluster as soon as a majority of master-eligible
nodes have joined so there is no benefit in waiting for any additional
master-eligible nodes to start.

*Impact* +
Discontinue use of the removed settings. If needed, use
`gateway.expected_data_nodes` or `gateway.recover_after_data_nodes` to defer
cluster recovery pending a certain number of data nodes.
====

.Legacy role settings have been removed.
[%collapsible]
====
*Details* +
The legacy role settings:

* `node.data`
* `node.ingest`
* `node.master`
* `node.ml`
* `node.remote_cluster_client`
* `node.transform`
* `node.voting_only`

have been removed. Instead, use the `node.roles` setting. If you were previously
using the legacy role settings on a 7.13 or later cluster, you will have a
deprecation log message on each of your nodes indicating the exact replacement
value for `node.roles`.

*Impact* +
Discontinue use of the removed settings. Specifying these settings in
`elasticsearch.yml` will result in an error on startup.
====

[[system-call-filter-setting]]
.The system call filter setting has been removed.
[%collapsible]
====
*Details* +
Elasticsearch uses system call filters to remove its ability to fork another
process. This is useful to mitigate remote code exploits. These system call
filters are enabled by default, and were previously controlled via the setting
`bootstrap.system_call_filter`. Starting in Elasticsearch 8.0, system call
filters will be required. As such, the setting `bootstrap.system_call_filter`
was deprecated in Elasticsearch 7.13.0, and is removed as of Elasticsearch
8.0.0.

*Impact* +
Discontinue use of the removed setting. Specifying this setting in Elasticsearch
configuration will result in an error on startup.
====

[[tier-filter-setting]]
.Tier filtering settings have been removed.
[%collapsible]
====
*Details* +
The cluster and index level settings ending in `._tier` used for filtering the allocation of a shard
to a particular set of nodes have been removed. Instead, the
{ref}/data-tier-shard-filtering.html#tier-preference-allocation-filter[tier
preference setting], `index.routing.allocation.include._tier_preference` should
be used. The removed settings are:

Cluster level settings:

- `cluster.routing.allocation.include._tier`
- `cluster.routing.allocation.exclude._tier`
- `cluster.routing.allocation.require._tier`

Index settings:

- `index.routing.allocation.include._tier`
- `index.routing.allocation.exclude._tier`
- `index.routing.allocation.require._tier`

*Impact* +
Discontinue use of the removed settings. Specifying any of these cluster settings in Elasticsearch
configuration will result in an error on startup. Any indices using these settings will have the
settings archived (and they will have no effect) when the index metadata is loaded.
====

[[shared-data-path-setting]]
.Shared data path and per index data path settings are deprecated.
[%collapsible]
====
*Details* +
Elasticsearch uses the shared data path as the base path of per index data
paths. This feature was previously used with shared replicas. Starting in
7.13.0, these settings are deprecated. Starting in 8.0 only existing
indices created in 7.x will be capable of using the shared data path and
per index data path settings.

*Impact* +
Discontinue use of the deprecated settings.
====

[[single-data-node-watermark-setting]]
.The single data node watermark setting is deprecated and now only accepts `true`.
[%collapsible]
====
*Details* +
In 7.14, setting `cluster.routing.allocation.disk.watermark.enable_for_single_data_node`
to false was deprecated. Starting in 8.0, the only legal value will be
true. In a future release, the setting will be removed completely, with same
behavior as if the setting was `true`.

If the old behavior is desired for a single data node cluster, disk based
allocation can be disabled by setting
`cluster.routing.allocation.disk.threshold_enabled: false`

*Impact* +
Discontinue use of the deprecated setting.
====

[[auto-import-dangling-indices-removed]]
.The `gateway.auto_import_dangling_indices` setting has been removed.
[%collapsible]
====
*Details* +
The `gateway.auto_import_dangling_indices` cluster setting has been removed.
Previously, you could use this setting to automatically import
{ref}/modules-gateway.html#dangling-indices[dangling indices]. However,
automatically importing dangling indices is unsafe. Use the
{ref}/indices.html#dangling-indices-api[dangling indices APIs] to manage and
import dangling indices instead.

*Impact* +
Discontinue use of the removed setting. Specifying the setting in
`elasticsearch.yml` will result in an error on startup.
====

.The `listener` thread pool has been removed.
[%collapsible]
====
*Details* +
Previously, the transport client used the thread pool to ensure listeners aren't
called back on network threads. The transport client has been removed
in 8.0, and the thread pool is no longer needed.

*Impact* +
Remove `listener` thread pool settings from `elasticsearch.yml` for any nodes.
Specifying `listener` thread pool settings in `elasticsearch.yml` will result in
an error on startup.
====

.The `fixed_auto_queue_size` thread pool type has been removed.
[%collapsible]
====
*Details* +
The `fixed_auto_queue_size` thread pool type, previously marked as an
experimental feature, was deprecated in 7.x and has been removed in 8.0.
The `search` and `search_throttled` thread pools have the `fixed` type now.

*Impact* +
No action needed.
====

.Several `transport` settings have been replaced.
[%collapsible]
====
*Details* +
The following settings have been deprecated in 7.x and removed in 8.0. Each setting has a replacement
setting that was introduced in 6.7.

- `transport.tcp.port` replaced by `transport.port`
- `transport.tcp.compress` replaced by `transport.compress`
- `transport.tcp.connect_timeout` replaced by `transport.connect_timeout`
- `transport.tcp_no_delay` replaced by `transport.tcp.no_delay`
- `transport.profiles.profile_name.tcp_no_delay` replaced by `transport.profiles.profile_name.tcp.no_delay`
- `transport.profiles.profile_name.tcp_keep_alive` replaced by `transport.profiles.profile_name.tcp.keep_alive`
- `transport.profiles.profile_name.reuse_address` replaced by `transport.profiles.profile_name.tcp.reuse_address`
- `transport.profiles.profile_name.send_buffer_size` replaced by `transport.profiles.profile_name.tcp.send_buffer_size`
- `transport.profiles.profile_name.receive_buffer_size` replaced by `transport.profiles.profile_name.tcp.receive_buffer_size`

*Impact* +
Use the replacement settings. Discontinue use of the removed settings.
Specifying the removed settings in `elasticsearch.yml` will result in an error
on startup.
====

.Selective transport compression has been enabled by default.
[%collapsible]
====
*Details* +
Prior to 8.0, transport compression was disabled by default. Starting in 8.0,
`transport.compress` defaults to `indexing_data`. This configuration means that
the propagation of raw indexing data will be compressed between nodes.

*Impact* +
Inter-node transit will get reduced along the indexing path. In some scenarios,
CPU usage could increase.
====

.Transport compression defaults to lz4.
[%collapsible]
====
*Details* +
Prior to 8.0, the `transport.compression_scheme` setting defaulted to `deflate`. Starting in
8.0,  `transport.compress_scheme` defaults to `lz4`.

Prior to 8.0, the `cluster.remote.<cluster_alias>.transport.compression_scheme`
setting defaulted to `deflate` when `cluster.remote.<cluster_alias>.transport.compress`
was explicitly configured. Starting in 8.0,
`cluster.remote.<cluster_alias>.transport.compression_scheme` will fallback to
`transport.compression_scheme` by default.

*Impact* +
This configuration means that transport compression will produce somewhat lower
compression ratios in exchange for lower CPU load.
====
//end::notable-breaking-changes[]

// This change is not notable because it should not have any impact on upgrades
// However we document it here out of an abundance of caution
[[fips-default-hash-changed]]
.When FIPS mode is enabled the default password hash is now PBKDF2_STRETCH
[%collapsible]
====
*Details* +
If `xpack.security.fips_mode.enabled` is true (see <<fips-140-compliance>>),
the value of `xpack.security.authc.password_hashing.algorithm` now defaults to
`pbkdf2_stretch`.

In earlier versions this setting would always default to `bcrypt` and a runtime
check would prevent a node from starting unless the value was explicitly set to
a "pbkdf2" variant.

There is no change for clusters that do not enable FIPS 140 mode.

*Impact* +
This change should not have any impact on upgraded nodes.
Any node with an explicitly configured value for the password hashing algorithm
will continue to use that configured value.
Any node that did not have an explicitly configured password hashing algorithm in
{es} 6.x or {es} 7.x would have failed to start.
====
