What’s New in ATS v10.2

This version of Apache Traffic Server™ includes 1039 commits from 655 pull requests, with 44 contributors participating in this development cycle.

Security Fixes

This release also contains all of the security fixes described in the July 2026 security advisory. Those fixes were committed directly to the release branch rather than through public pull requests, so they do not carry PR numbers; they are listed by commit subject at the end of CHANGELOG-10.2.0. Refer to the advisory for the CVE identifiers, severities, and affected version ranges.

Configuration Reload

Configuration reload has been rebuilt around a token model that makes a reload an observable, trackable operation rather than a fire-and-forget signal. Each reload gets a token; handlers report progress and terminal state against that token, so a reload can be monitored to completion and its per-handler logs inspected. See Configuration Reload Framework.

traffic_ctl config reload gained --monitor/-m to follow a reload to completion, --show-details/-s and --include-logs/-l for per-handler detail, --token/-t to target a specific token, --refresh-int/-r and --timeout/-T to control polling, and --force/-F.
traffic_ctl config status reports reload records for a token, with --count/-c (numeric or all) and --min-level to filter log severity.
Reload behavior is tunable with proxy.config.admin.reload.timeout and proxy.config.admin.reload.check_interval.
Replaced configurations are now destroyed on an ET_TASK thread rather than on a network thread, so a large config teardown no longer blocks an event loop.

Shared-Memory Cache Directory (Fast Restart)

The cache directory — the memory-resident index mapping cached objects to their location on disk — is normally rebuilt from disk on every start, which takes minutes on a large cache. It can now be hosted in POSIX shared memory so the next process start attaches the existing segment in milliseconds instead of rebuilding it.

Recovery is fail-safe: anything untrustworthy (crash, reboot, ABI or schema mismatch, failed validation, bad disk) falls back to the existing disk-rebuild path, and cache reads still validate the Doc magic and key, so a stale entry is a miss rather than served corruption.

The feature is opt-in and defaults to off, making it a functional no-op unless enabled:

traffic_ctl cache shm status and traffic_ctl cache shm clear inspect and drop the segment. See Shared-Memory Cache Directory (Fast Restart) for the design, recovery model and platform notes.

Features

traffic_ctl cache clear performs a logical cache purge by advancing the global HTTP cache generation, so a cache reset no longer requires restarting Traffic Server or hand-editing the cache generation. It is backed by a restricted JSONRPC method. See traffic_ctl cache and admin_cache_clear.
Implement RFC 9213 Targeted HTTP Cache Control. Cache directives can be targeted at specific caches via headers such as CDN-Cache-Control, configured through proxy.config.http.cache.targeted_cache_control_headers, which is overridable per remap rule. When a targeted header is present it takes precedence over the standard Cache-Control header, and the targeted header is passed downstream so cache hierarchies behave correctly.
Connect retries to the origin can now back off exponentially, controlled by proxy.config.http.connect_attempts_retry_backoff_base, instead of retrying immediately and piling connections onto a struggling origin.
Origin connect retry limits are now selected by HostDB state: proxy.config.http.connect_attempts_max_retries for UP servers, the new proxy.config.http.connect_attempts_max_retries_suspect_server for SUSPECT, and no retries for DOWN. The retry limits were not previously applied according to origin state, so this is a necessary incompatible change. See Upgrading to ATS v10.2 before deploying.
proxy.config.http.connect.down.policy gained option 3, which counts inactive connections as failures.
Snowflake IDs, 64-bit organizationally unique identifiers, are now used for connection IDs so they are unique across restarts and typically across instances in a CDN.
TLS certificate compression is supported in both directions, configured with proxy.config.ssl.server.cert_compression.algorithms and proxy.config.ssl.client.cert_compression.algorithms.
Certificate loading can now be parallelized with proxy.config.ssl.server.multicert.concurrency.
sni.yaml supports session ticket overrides.
QUIC token secrets are configurable via proxy.config.quic.server.token_key.filename.
The PROXY protocol header size limit is configurable with proxy.config.proxy_protocol.max_header_size.
A per-client connection limit exempt list is available through proxy.config.http.per_client.connection.exempt_list, the new connection_exempt_list plugin, and the TS API (see below).
Parsed values for expensive STRING configurations (for example negative_caching_list, insert_forwarded, server_session_sharing.match) are now cached automatically, so repeated TSHttpTxnConfigStringSet() calls with the same value parse only once.
The migration from PCRE to PCRE2 is complete; all remaining PCRE references have been removed from the core and plugins.

Configuration

New records.yaml settings in this release:

Other configuration changes:

proxy.config.ssl.max_record_size now accepts the documented -1 value, making dynamic TLS record sizing reachable from records.yaml.
proxy.config.ssl.client.CA.cert.filename is now overridable.
negative_caching_list and negative_revalidating_list are overridable.
traffic_ctl config reset resets configuration values matching a path pattern back to their defaults.
traffic_ctl hostdb status is a new command for inspecting HostDB state.
traffic_ctl gained a global --watch/-w option to re-run a command periodically.
JSONRPC now refuses writes to records marked RECA_READ_ONLY or RECA_NO_ACCESS.

Metrics

Added proxy.process.http.000_responses
Added proxy.process.http.429_responses
Added proxy.process.log.marshalled_bytes
Added proxy.process.net.per_client.connections_exempt_in
Added proxy.process.ssl.connections_closed
Added proxy.process.ssl.total_handshake_bytes_read_in
Added proxy.process.ssl.total_handshake_bytes_write_out
Added proxy.process.ssl.ssl_session_cache_timeout
Added proxy.process.ssl.ssl_origin_session_cache_timeout
Added proxy.process.ssl.handshake_sign_rsa, proxy.process.ssl.handshake_sign_ecdsa and proxy.process.ssl.handshake_sign_other to count handshake signatures by key type
Added TLS certificate compression counters proxy.process.ssl.cert_compress.{zlib,brotli,zstd} and proxy.process.ssl.cert_decompress.{zlib,brotli,zstd}, each with a matching _failure counter
Added proxy.process.plugin.header_rewrite.conditions and proxy.process.plugin.header_rewrite.operators
Added proxy.process.plugin.compress.bytes_in
Added per-plugin workload counters under the proxy.process.plugin. prefix
Added per-curve TLS handshake time metrics and a cache stripe lock contention metric
proxy.process.http.incoming_requests is now counted at transaction start

Logging

New log fields in this release:

chiv - verified client host IP
ckh - cache key hash
cqqtl - client request squid length including TLS overhead
cqssrt - TLS session resumption type
cthb, cthbr, cthbt - client TLS handshake bytes (total, received, transmitted)
mstsms - server-side TLS handshake milestone
pptc, pptg, pptv - PROXY protocol TLS cipher, group and version
prscs - the component that set the proxy response status code
psfid - process Snowflake ID
psqtl - proxy response squid length including TLS overhead

Other logging changes:

Plugins can register custom log fields at runtime with TSLogFieldRegister and the TSLog*Marshal functions.
Added the ERR_TUN_ACTIVE_TIMEOUT squid code for tunnel timeouts.

Plugins

New plugins:

connection_exempt_list - manage the per-client connection limit exempt list
filter_body - filter request and response body content
jax_fingerprint - consolidated JA3/JA4 fingerprinting
realip - set the verified client address from a trusted source

redo_cache_lookup has been moved out of the experimental plugins and into the examples.

header_rewrite and hrw4u:

hrw4u is a new DSL and compiler for header_rewrite configurations, with a companion u4wrh tool that converts existing header_rewrite configuration back into the DSL. See HRW4U DSL.
header_rewrite can invoke the hrw4u compiler directly at config load.
Added elif support in if/elif/else chains, nested if, SETS with partial string matching, session-scope state variables, SERVER-HEADER and SERVER-URL, indexed query parameters, set-effective-address, set-cc-alg, and POST_REMAP_HOOK support.
Per-remap MaxMind geo database handles are supported.
Bad run-plugin directives are now rejected at config load rather than at runtime.

Other plugin changes:

compress: Zstandard support, content-type parameter handling, and an option to skip compressing partial objects.
stats_over_http: a Prometheus v2 output format that groups samples by metric family and derives labels for methods, directions, status codes, cache results, time buckets and cache volumes; plus HINT and TYPE annotations.
xdebug: a probe-full-json feature that emits the full probe output as JSON, including the encoded origin body.
escalate: added the x-escalate-redirect header and --escalate-non-get-methods.
esi: added --allowed-response-codes.
maxmind_acl: added a bypass header configuration option.
slice: prefetch deduplication and a freelist, and purge now covers every block of an object rather than stopping at the first gap.
lua: support for Unix domain socket inbound connections, the verified address API, PROXY protocol info, certificate introspection, the connection exempt list, and a shutdown hook.
Cripts: cache group concepts, geo APIs on cripts::IP, a refactored cache key / URL API, and a substantially smaller per-transaction Context.

TS API

TSVConnClientHelloGet and TSClientHelloExtensionGet provide access to the TLS ClientHello and its extensions.
TSHttpTxnVerifiedAddrSet / TSHttpTxnVerifiedAddrGet set and read a verified client address.
TSHttpTxnCacheKeyDigestGet returns the cache key hash.
TSLogFieldRegister, TSLogIntMarshal, TSLogStringMarshal and TSLogAddrMarshal allow plugins to define custom log fields.
TSConnectionLimitExemptListAdd, TSConnectionLimitExemptListRemove and TSConnectionLimitExemptListClear manage the per-client connection limit exempt list.
TSHttpTxnNextHopStrategySet, TSHttpTxnNextHopStrategyGet and TSHttpTxnParentStrategyGet expose next hop strategy selection.
TSMutexLockGuard is an RAII guard for TSMutex.

What’s New in ATS v10.1

Metrics

Added proxy.process.http.total_parent_marked_down_timeout
Added proxy.process.http.total_client_connections_uds
Added proxy.process.ssl.group.user_agent.P-256
Added proxy.process.ssl.group.user_agent.P-384
Added proxy.process.ssl.group.user_agent.P-521
Added proxy.process.ssl.group.user_agent.X25519
Added proxy.process.ssl.group.user_agent.P-224
Added proxy.process.ssl.group.user_agent.X448
Added proxy.process.ssl.group.user_agent.X25519MLKEM768

Plugins

stats_over_http: Add prometheus metrics format option
header_rewrite: Add set-plugin-cntl operator
header_rewrite: Add LAST-CAPTURE condition to access the last capture group of a regex
header_rewrite: Add support for state variables that can be used in conditions and operators.
header_rewrite: Add support for an else clause in conditions
header_rewrite: Add a GROUP condition
header_rewrite: Add a HTTP-CNTL condition to control if expensive rules are run.
header_rewrite: Add the set-body-from operator to set the response body from a URL
header_rewrite: The set-body-from operator now defers renabling the transaction until after the fetch of the URL providing the response body
slice: Support unix domain socket paths
slice: Add configuration to limit slicing of some objects.
access_control: Generate a session cookie when exp=0 appears in a TokenRespHdr origin response header.
compress: Add range request control options to adjust behavior based on the Accept-Encoding or Range headers
lua: Add support for millisecond sleep
escalate: Now handles dispatching to the failover server if the original server is down
ja3_fingerprint: Add the --preserve option to avoid modifing some existing ja* fields.
ja4_fingerprint: Added this new plugin
rate_limit: Add a --rate option to limit by RPS

TS API

Add TSVConnPPInfoGet to get Proxy Protocol information.
Add TSContScheduleOnEntirePool and TSContScheduleEveryOnEntirePool to schedule continuations on every thread in a pool.

Features

Add the cqssg log field for TLS group name logging
traffic_ctl: Add a new server command to show some basic internal information
traffic_ctl: Now displays YAML format output when the --records option is set.
traffic_ctl: Added the server debug command to enable/disable diagnostics and debug tags at runtime with a single command.
cripts: Add some new high level convenience APIs
cripts: Add optional reason parameter to Error::Status
sni.yaml: Add server_cipher_suite and server_TLSv1_3_cipher_suites to allow overriding the setting from records.yaml
Add support for getting authority information from Proxy Protocol V2. with new ppa log formatter.
Add support for getting UDP address info from Proxy Protocol.
Added support for listening on a Unix Domain Socket. See proxy.config.http.server_ports
Added option for proxy.config.http.auth_server_session_private to only mark the connection private if Proxy-Authorization or Www-Authenticate headers are present
It is now an ERROR if a remap ACL has more than one @action parameter. This was an error in ATS 10.0.x
Add a fragment-size option in volume.config to control the fragment size of the volume.
Add an optional avg_obj_size to volume.config to control the directory entry sizing.
The proxy.config.http.cache.post_method is now an overridable config.
Defer deleting the copied plugin shared object file to startup to make it easier to debug crashes in plugins.

Configuration

Added proxy.config.http.negative_revalidating_list to configure the list of status codes that apply to the negative revalidating feature
Added proxy.config.ssl.session_cache.mode to control TLS session caching. This is intended to replace the legacy proxy.config.ssl.session_cache.enabled and proxy.config.ssl.session_cache.value configurations. The proxy.config.ssl.session_cache.enabled setting was documented but never implemented, while proxy.config.ssl.session_cache.value was implemented but not documented. The new proxy.config.ssl.session_cache.mode functions just like the legacy proxy.config.ssl.session_cache.value did in the ealier 10.0 release. The proxy.config.ssl.session_cache.mode setting provides a clear and consistent interface going forward. For backward compatibility, .enabled is now implemented, but both .enabled and .value will be removed in ATS 11.x.

What’s New in ATS v10.0

This version of Apache Traffic Server™ includes over <x> commits, from <y> pull requests. A total of <z> contributors have participated in this development cycle.

New Features

JSON-RPC based interface for administrative API

Traffic Server now exposes a JSON-RPC node to interact with external tools. Check JSONRPC for more details.
traffic_ctl has a new command monitor to show a continuously updating list of metrics
ip_allow.yaml and remap.config now support named IP ranges via IP Categories. See the ip_categories key definition in ip_allow.yaml for information about their use and definitions.
sni.yaml fqdn:tunnel_route, beside the already supported match group number, configuration now also supports the destination port using a variable specification either for the incoming connection port or the port that was specified by the incoming Proxy Protocol payload. Check sni.yaml for more information.
The records.yaml entry proxy.config.system_clock was added to control the underlying system clock that ATS uses for internal timing
OCSP requests is now be able to use GET method. See proxy.config.ssl.ocsp.request_mode for more information.
TSHttpSsnInfoIntGet has been added.

New or modified Configurations

ip_allow.yaml and remap.config ACL actions

There are two new sets of actions for HTTP request method filtering introduced in Traffic Server 10.x:

Both ip_allow.yaml and remap.config now support the set_allow and set_deny actions. These actions both behave like allow and deny did for ip_allow.yaml pre Traffic Server 10.x.
In addition, remap.config now supports add_allow and add_deny actions. These behave like allow and deny actions did for remap.config ACLs pre Traffic Server 10.x.

The details about the motivation and behavior of these actions are documented in ACL Filters.

Logging and Metrics

The numbers of HTTP/2 frames received have been added as metrics.

Plugins

authproxy - --forward-header-prefix parameter has been added
prefetch - Cmcd-Request header support has been added
xdebug - --enable option to selectively enable features has been added
system_stats - Stats about memory have been added
slice plugin - This plugin was promoted to stable.
compress plugin - Added support for Zstandard (zstd) compression algorithm.

JSON-RPC

Remote clients, like traffic_ctl have now bi-directional access to the plugin space. For more details check Handler implementation.

Replaced autotools build system with cmake

See Installing Traffic Server for more information

Switch to C++20

Plugins are now required to be compiled as C++ code, rather than straight C. The API is tested with C++20, so code compatible with this version is preferred. TSDebug and related functions are removed. Debug tracing should now be done using cpp:func:Dbg and related functions, as in Traffic Server core code.

C++ Plugin API Deprecated

It is deprecated in this release. It will be deleted in ATS 11.

Symbols With INKUDP Prefix

In the plugin API, all types and functions starting with the prefix INKUDP are removed.

New plugin hook for request sink transformation

A new hook, TS_HTTP_REQUEST_CLIENT_HOOK, has been added. This provides the analoguas functionality of TS_HTTP_RESPONSE_CLIENT_HOOK, for request bodies.

HTTP/2

Support for HTTP/2 on origin server connections has been added. This is disabled by default. For more details check proxy.config.ssl.client.alpn_protocols
Support for CONNECT method has been added.
Window size control has been improved. For more details check proxy.config.http2.flow_control.policy_in

HTTP UI Removed

The stats and cache inspector pages were unmaintained and removed in this release.