Downgraded version of docker-compose files to 3.3 (instead 3.4) since VSTS agent still doesn't support it plus other versions of Docker. We'll upgrade to 3.4 soon, though. When VSTS supports it.

Error in VSTS:
3 error(s), 1 warning(s)
Phase 1 - 3 error(s), 1 warning(s)
Version in "/opt/vsts/work/1/s/docker-compose.yml" is unsupported. You might be seeing this error because you're using the wrong Compose file version. Either specify a supported version (e.g "2.2" or "3.3") and place your service definitions under the `services` key, or omit the `version` key and place your service definitions at the root of the file to use version 1.
For more on the Compose file format versions, see https://docs.docker.com/compose/compose-file/
/usr/local/bin/docker-compose failed with return code: 1

docker-compose-external.override.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 services:
   sql.data:

docker-compose-external.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 services:
   sql.data:

docker-compose-windows.prod.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 # The Production docker-compose file has to have the external/real IPs or DNS names for the services 
 # The ESHOP_PROD_EXTERNAL_DNS_NAME_OR_IP environment variable is taken, by default, from the ".env" file defined like: 

docker-compose-windows.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 services:
   basket.api:

docker-compose.ci.build.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 services:
   ci-build:

docker-compose.nobuild.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 services:
   basket.api:

docker-compose.override.windows.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 # ONLY NEEDED WHEN RUNNING WINDOWS CONTAINERS
 #

docker-compose.override.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 # The default docker-compose.override file can use the "localhost" as the external name for testing web apps within the same dev machine. 
 # The ESHOP_EXTERNAL_DNS_NAME_OR_IP environment variable is taken, by default, from the ".env" file defined like: 

docker-compose.prod.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 # The Production docker-compose file has to have the external/real IPs or DNS names for the services 
 # The ESHOP_PROD_EXTERNAL_DNS_NAME_OR_IP environment variable is taken, by default, from the ".env" file defined like: 

docker-compose.yml

@@ -1,4 +1,4 @@
-version: '3.4'
+version: '3.3'
 
 services: