Changes in Varnish 7.1

For information about updating your current Varnish deployment to the new version, see Upgrading to Varnish 7.1.

A more detailed and technical account of changes in Varnish, with links to issues that have been fixed and pull requests that have been merged, may be found in the change log.



A new kind of parameters exists: deprecated aliases. Their documentation is minimal, mainly referring to the actual symbols they alias. They are not listed in the CLI, unless referred to explicitly.

There is no deprecated alias yet, but some are already planned for future releases. Alias parameters have next to no overhead when used directly.

The deprecated vsm_space parameter was removed.

A new cc_warnings parameter contains a subset of the compiler flags extracted from cc_command, which in turn grew new expansions:

  • %d: the raw default cc_command

  • %D: the expanded default cc_command

  • %w: the cc_warnings parameter

  • %n: the working directory (-n option)

This should facilitate the creation of wrapper scripts around VCL compilation.

There is a new experimental parameter that is identical to the feature parameter, except that it guards features that may not be considered complete or stable. An experimental feature may be promoted to a regular feature or dropped without being considered a breaking change.

Command line options

The deprecated sub-argument of the -l option was removed, it is now a shorthand for the vsl_space parameter only.

The -T, -M and -P command line options can be used multiple times, instead of retaining only the last occurrence.

When there is no active VCL, the first loaded VCL was always implicitly used too. This is now only true for VCLs loaded with either the -f or -b options, since they imply a vcl.use. VCL loaded through the Varnish CLI (vcl.load or vcl.inline) via a CLI script loaded through the -I command line option require an explicit vcl.use.

Other changes in varnishd

ESI includes now support the onerror="continue" attribute. However, in order to take effect a new +esi_include_onerror feature flag needs to be raised.

Changes to VCL

It is now possible to assign a BLOB value to a BODY variable, in addition to STRING as before.

VCL variables

New VCL timestamp variables have been added to track the point in time when HTTP messages were created:

  • req.time

  • req_top.time

  • resp.time

  • bereq.time

  • beresp.time

  • obj.time

The new req.transport variable returns “HTTP/1” or “HTTP/2” as appropriate.

Other changes to VCL

Where a regular expression literal is expected, it is now possible to have a concatenation of constant strings. It can be useful when part of the expression comes from an environment-specific include, or to break a long expression into multiple lines. (introduced with 7.0.1)

Similarly to varnishd parameters, it is now possible to have deprecated aliases of VCL variables. Although there are none so far, aliases will allow some symbols to be renamed without immediately breaking existing VCL code.

Deprecated VCL aliases have no runtime overhead, they are reified at VCL compile time.


New STRING strftime(TIME time, STRING format) function for UTC formatting.

It is now possible to declare deprecated aliases of VMOD functions and object methods, just like VCL aliases. The cookie.format_rfc1123() function was renamed to STRING format_date(TIME now, DURATION timedelta), and the former was retained as a deprecated alias of the latter for compatibility.

Deprecated VMOD aliases have no runtime overhead, they are reified at VCL compile time.


It is now possible to write to the standard output with -w -, to be on par with the ability to read from the standard input with -r -. This is not possible in daemon mode.

In a pipe scenario, the backend transaction emits a Start timestamp and both client and backend transactions emit the Process timestamp.


It is now possible to write to the standard output with -w -, to be on par with the ability to read from the standard input with -r -. This is not possible in daemon mode.


When is invoked without a parameter, it defaults to the active VCL.

The param.set command accepts a -j option. In this case the JSON output is the same as -j of the updated parameter.

A new debug.shutdown.delay command is available in the Varnish CLI for testing purposes. It can be useful for testing purposes to see how its environment (service manager, container orchestrator, etc) reacts to a varnishd’s child process taking significant time to stop.


The SO_RCVTIMEO_WORKS feature check is gone. (introduced with 7.0.1)

The reporting of logexpect events was rearranged for readability.

The abort command in the logexpect facility of varnishtest can now be used to trigger an abort() to help debugging the vsl client library code.

The vtc.barrier_sync() VMOD function can be used in vcl_init from now on.

Changes for developers and VMOD authors

The SO_RCVTIMEO and SO_SNDTIMEO socket options are now required at build time since their absence would otherwise prevent some timeouts to take effect. We no longer check whether they effectively work, hence the removal of the SO_RCVTIMEO_WORKS feature check in varnishtest. (introduced with 7.0.1)

Varnish will use libunwind by default when available at configure time, the --without-unwind configure flag can prevent this and fall back to libexecinfo to generate backtraces.

There is a new debug storage backend for testing purposes. So far, it can only be used to ensure that allocation attempts return less space than requested.

There are new C macros for VCL_STRANDS creation: TOSTRAND() and TOSTRANDS() are available in vrt.h.

New utility macros vmin[_t], vmax[_t] and vlimit[_t] available in vdef.h.

The fetch and delivery filters should now be registered and unregistered with VRT_AddFilter() and VRT_RemoveFilter().

Dynamic backends are now reference-counted, and VMOD authors must explicitly track assignments with VRT_Assign_Backend().

The vtc.workspace_reserve() VMOD function will zero memory from now on.

When the +workspace debug flag is raised, workspace logs are no longer emitted as raw logs disconnected from the task. Having workspace logs grouped with the rest of the task should help workspace footprint analysis.

It is now possible to generate arbitrary log lines with vtc.vsl() and vtc.vsl_replay(), which can help testing log processing utilities.

It is also possible to tweak the VXID cache chunk size per thread pool with the debug.xid command for the Varnish CLI, which can also help testing log processing utilities.

http_IsHdr() is now exposed as part of the strict ABI for VMODs.

Platform Support


With the End of Life of CentOS 8, we will build el8 packages on almalinux from now on. This means that we will always target the oldest el8 branch. For example a package built for el8.5 is not guaranteed to work on el8.1 even though the latter may still be supported by Red Hat.


The kill mode of the varnish service was changed from process to mixed to ensure that the cache process is killed if the manager process is timed out by systemd. Otherwise, a race exists with the cache process where a restart is carried on before the old cache process exits, creating conflict on resources such as listen ports.