+h3. Multi-file docker image collections
+
+Typically a docker image collection contains a single @.tar@ file at the top level. Handling of atypical cases has changed. If a docker image collection contains files with extensions other than @.tar@, they will be ignored (previously they could cause errors). If a docker image collection contains multiple @.tar@ files, it will cause an error at runtime, "cannot choose from multiple tar files in image collection" (previously one of the @.tar@ files was selected). Subdirectories are ignored. The @arv keep docker@ command always creates a collection with a single @.tar@ file, and never uses subdirectories, so this change will not affect most users.
+
+h3. New spelling of S3 credential configs
+
+If you use the S3 driver for Keep volumes and specify credentials in your configuration file (as opposed to using an IAM role), you should change the spelling of the @AccessKey@ and @SecretKey@ config keys to @AccessKeyID@ and @SecretAccessKey@. If you don't update them, the previous spellings will still be accepted, but warnings will be logged at server startup.
+
+h3. New proxy parameters for arvados-controller
+
+In your Nginx configuration file (@/etc/nginx/conf.d/arvados-api-and-controller.conf@), add the following lines to the @location /@ block with @http://controller@ (see "Update nginx configuration":{{site.baseurl}}/install/install-api-server.html#update-nginx for an example) and reload/restart Nginx (@sudo nginx -s reload@).
+
+<pre>
+ proxy_set_header Upgrade $http_upgrade;
+ proxy_set_header Connection "upgrade";
+</pre>
+
+h3. Changes on the collection's @preserve_version@ attribute semantics
+
+The @preserve_version@ attribute on collections was originally designed to allow clients to persist a preexisting collection version. This forced clients to make 2 requests if the intention is to "make this set of changes in a new version that will be kept", so we have changed the semantics to do just that: When passing @preserve_version=true@ along with other collection updates, the current version is persisted and also the newly created one will be persisted on the next update.
+
+h3. System token requirements
+
+System services now log a warning at startup if any of the system tokens (@ManagementToken@, @SystemRootToken@, and @Collections.BlobSigningKey@) are less than 32 characters, or contain characters other than a-z, A-Z, and 0-9. After upgrading, run @arvados-server config-check@ and update your configuration file if needed to resolve any warnings.
+
+The @API.RailsSessionSecretToken@ configuration key has been removed. Delete this entry from your configuration file after upgrading.
+