- .NET core 2.2 linux base images were flagged for security vulnerabilities and no updates available
- move to .NET Core 2.1 base images with long time support, so ACR can auto update.

- addressed the following CVE/DSA (list may not be complete):
- DSA4685-1, DLA2290-1, DSA4646-1, DSA4633-1, DSA4666-1, DLA2295-1
- CVE-2020-3810, CVE-2019-5188, CVE-2020-10531, CVE-2019-5436, CVE-2019-5481, CVE-2019-5482, CVE-2020-12243, CVE-2020-8177

Bugfix: drop messages that can't send to IoT Hub and report total number of dropped messages instead of increasing memory

Bugfix for batch interval.

Which configurations are being added to publisher?

Publisher will support 2 configurations – (1) batch size, number of subscription notifications in a batch and (2) batch interval, a length of time since the last batch was sent. A subscription notification can contain “n” number of values from the endpoint subscription which depending on the combined size could result in 1 to more IoT Hub messages.

How can these configurations be set?

The configs are exposed as environment variables on the Publisher container Pod and they affect all job configurations using the Publisher REST API (iot/opc-publisher-service). The publisher container must be restarted for any changes in the environment variable to take effect.

PCS_DEFAULT_PUBLISH_JOB_BATCH_INTERVAL can be set as milliseconds from 100 to 3,600,000 ms.  Other values (e.g. <= 0) will result in the default value of 10,000 ms (10 seconds).

PCS_DEFAULT_PUBLISH_JOB_BATCH_SIZE can be set as a value between 2 and 1000.  Every other value will result in the default of 50 OPC UA subscription notifications per batch. OPC publisher partitions the number of configured tags in a publish job on a 1000 boundary, i.e. every subscription has at most 1000 monitored items (variables).  It is recommended to leave this value at 50.

 * Allow environment variable configuration of batch size and interval.
     The following environment variables can be set to configure the batch trigger interval and batch size.
     The environment variable PCS_DEFAULT_PUBLISH_JOB_BATCH_INTERVAL can be set as milliseconds from 100 to 3,600,000 ms.  Other values (e.g. <= 0) will result in the default value of 10,000 ms (10 seconds).
     The environment variable PCS_DEFAULT_PUBLISH_JOB_BATCH_SIZE can be set as a value between 2 and 1000.   Every other value will result in the default of 50 subscription notifications per batch being set.
     The environment variables must be set on the Publisher container Pod to affect the settings in all job configurations from this point on that are performed using the Publisher REST API.  (iot/opc-publisher-service).
     The change is in the PublisherJobService Adapter, which adapts from 2.7 REST API to internal Publisher configuration API.  The engine configuration that had hardcoded settings in them in 2.7 release will be updated to read both values out of the environment and set them in the configuration.
 * Use foreach to send messages vs bulk to send batches as bulk can cause errors when combined is greater than 256k
 * Robustness for batching logic