Upgrading to Varnish 6.2


VCL programs for Varnish 6.1 can be expected to run without changes in the new version.

A VCL load will now issue a warning, but does not fail as previously, if a backend declaration uses the .path field to specify a Unix domain socket, but the socket file does not exist or is not accessible at VCL load time. This makes it possible to start the peer component listening at the socket, or set its permissions, after Varnish starts or the VCL is loaded. Backend fetches fail if the socket is not accessible by the time the fetch is attempted.

return(miss) from vcl_hit{} is now removed. An option for implementing similar functionality is:

  • return (restart) from vcl_hit{}
  • in vcl_recv{} for the restart (when req.restarts has increased), set req.hash_always_miss = true;.

Runtime parameters

Some varnishd -p parameters that have been deprecated for some time have been removed. If you haven't changed them yet, you have to now. These are:

The default value of thread_pool_stack has been increased from 48k to 56k on 64-bit platforms and to 52k on 32-bit platforms. See the discussion under Parameters in Changes in Varnish 6.2 for details.

Type conversion functions in VMOD std

The existing type-conversion functions in VMOD std - Varnish Standard Module have been reworked to make them more flexible and easier to use. These functions now also accept suitable numeral or quantitative arguments.

These type-conversion functions should be fully backwards compatible, but the following differences should be noted:

  • The fallback is not required any more. A conversion failure in the absence of a fallback argument will now trigger a VCL failure.
  • A VCL failure will also be triggered if no or more than one argument (plus optional fallback) is given.
  • Conversion functions now only ever truncate if necessary (instead of rounding).
  • REAL round(REAL r) has been added for explicit rounding.

The following functions are deprecated and should be replaced by the new conversion functions:

They will be removed in a future version of Varnish.

varnishadm and the CLI

The -j option for JSON output has been added to a number of commands, see JSON output in Changes in Varnish 6.2 and varnish-cli. We recommend the use of JSON format for automated parsing of CLI responses (varnishadm output).

Listing backends

backend.list has grown an additional column, the output has changed and fields are now of dynamic width:

  • The Admin column now accurately states probe only if a backend has some means of dynamically determining health state.

  • The Probe column has been changed to display X/Y, where:

    • Integer X is the number of good probes in the most recent window; or if the backend in question is a director, the number of healthy backends accessed via the director or any other director-specific metric.
    • Integer Y is the window in which the threshold for overall health of the backend is defined (from the .window field of a probe, see VCL); or in the case of a director, the total number of backends accessed via the director or any other director-specific metric.

    If there is no probe or the director does not provide details, 0/0 is output.

  • The Health column has been added to contain the dynamic (probe) health state and the format has been unified to just healthy or sick.

    If there is no probe, Health is always given as healthy. Notice that the administrative health as shown in the Admin column has precedence.

In the probe_message field of backend.list -j output, the Probe and Health columns appear as the array [X, Y, health].

See varnish-cli for details.

Listing VCLs

The non-JSON output of vcl.list has been changed:

  • The state and temperature fields appear in separate columns (previously combined in one column).
  • The optional column showing the relationships between labels and VCL configurations (when labels are in use) has been separated into two columns.

See varnish-cli for details. In the JSON output for vcl.list -j, this information appears in separate fields.

The width of columns in backend.list and vcl.list output (non-JSON) is now dynamic, to fit the width of the terminal window.

For developers and authors of VMODs and API clients

Python 3.4 or later is now required to build Varnish, or use scripts installed along with Varnish, such as vmodtool.py to build VMODs or other Varnish artifacts. Python 2 is no longer supported, and this support will likely be dropped in a future 6.0 LTS release too.

The VRT API has been bumped to version 9.0. Changes include:

  • Functions in the API have been added, and others removed.
  • The VCL_BLOB type is now implemented as struct vrt_blob.
  • The req_bodybytes field of struct req has been removed, and should now be accessed as an object core attribute.

See vrt.h, the change log and Directors in Changes in Varnish 6.2 for details.

The vmodtool has been changed significantly to avoid name clashes in the C identifiers declared in vcc_if.h. This may necessitate changing names in your VMOD code. To facilitate renaming, vcc_if.h defines macros for prepending the vmod prefix, and for naming enums and argument structs. For details, see the change log, and examine the contents of vcc_if.h after generation.

Going forward, we will adhere to the principle that data returned by VMOD methods and functions are immutable. This is now enforced in some places by use of the const modifier. A VMOD is free to do as it sees fit within its own implementation, but if you attempt to change something returned by another VMOD, the results are undefined.