diff --git a/result/dotnet/Dockerfile.1809 b/result/dotnet/Dockerfile.1809
index 8595143..9020c04 100644
--- a/result/dotnet/Dockerfile.1809
+++ b/result/dotnet/Dockerfile.1809
@@ -1,4 +1,4 @@
-FROM  mcr.microsoft.com/dotnet/core/sdk:2.1 as builder
+FROM  mcr.microsoft.com/dotnet/core/sdk:3.1 as builder
 
 WORKDIR /Result
 COPY Result/Result.csproj .
@@ -8,7 +8,7 @@ COPY /Result .
 RUN dotnet publish -c Release -o /out Result.csproj
 
 # app image
-FROM mcr.microsoft.com/dotnet/core/aspnet:2.1
+FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
 
 WORKDIR /app
 ENTRYPOINT ["dotnet", "Result.dll"]
diff --git a/result/dotnet/Result/Result.csproj b/result/dotnet/Result/Result.csproj
index c004a55..d48265f 100644
--- a/result/dotnet/Result/Result.csproj
+++ b/result/dotnet/Result/Result.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/vote/dotnet/Dockerfile.1809 b/vote/dotnet/Dockerfile.1809
index a4f8685..a4acef3 100644
--- a/vote/dotnet/Dockerfile.1809
+++ b/vote/dotnet/Dockerfile.1809
@@ -1,4 +1,4 @@
-FROM mcr.microsoft.com/dotnet/core/sdk:2.1 as builder
+FROM mcr.microsoft.com/dotnet/core/sdk:3.1 as builder
 
 WORKDIR /Vote
 COPY Vote/Vote.csproj .
@@ -8,7 +8,7 @@ COPY /Vote .
 RUN dotnet publish -c Release -o /out Vote.csproj
 
 # app image
-FROM mcr.microsoft.com/dotnet/core/aspnet:2.1
+FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
 
 WORKDIR /app
 ENTRYPOINT ["dotnet", "Vote.dll"]
diff --git a/vote/dotnet/Vote/Vote.csproj b/vote/dotnet/Vote/Vote.csproj
index 479b76e..3a80a2a 100644
--- a/vote/dotnet/Vote/Vote.csproj
+++ b/vote/dotnet/Vote/Vote.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/worker/Dockerfile b/worker/Dockerfile
index 788a738..89739f8 100644
--- a/worker/Dockerfile
+++ b/worker/Dockerfile
@@ -1,4 +1,4 @@
-FROM mcr.microsoft.com/dotnet/core/sdk:2.1 as builder
+FROM mcr.microsoft.com/dotnet/core/sdk:3.1 as builder
 
 WORKDIR /Worker
 COPY src/Worker/Worker.csproj .
@@ -8,7 +8,7 @@ COPY src/Worker/ .
 RUN dotnet publish -c Release -o /out Worker.csproj
 
 # app image
-FROM mcr.microsoft.com/dotnet/core/runtime:2.1
+FROM mcr.microsoft.com/dotnet/core/runtime:3.1
 
 WORKDIR /app
 ENTRYPOINT ["dotnet", "Worker.dll"]
diff --git a/worker/dotnet/Dockerfile.1809 b/worker/dotnet/Dockerfile.1809
index c5f52c3..4f1b9d2 100644
--- a/worker/dotnet/Dockerfile.1809
+++ b/worker/dotnet/Dockerfile.1809
@@ -1,4 +1,4 @@
-FROM mcr.microsoft.com/dotnet/core/sdk:2.1 as builder
+FROM mcr.microsoft.com/dotnet/core/sdk:3.1 as builder
 
 WORKDIR /Worker
 COPY Worker/Worker.csproj .
@@ -8,7 +8,7 @@ COPY /Worker .
 RUN dotnet publish -c Release -o /out Worker.csproj
 
 # app image
-FROM mcr.microsoft.com/dotnet/core/runtime:2.1
+FROM mcr.microsoft.com/dotnet/core/runtime:3.1
 
 WORKDIR /app
 ENTRYPOINT ["dotnet", "Worker.dll"]
diff --git a/worker/dotnet/Worker/Worker.csproj b/worker/dotnet/Worker/Worker.csproj
index 46ec2db..d85a98c 100644
--- a/worker/dotnet/Worker/Worker.csproj
+++ b/worker/dotnet/Worker/Worker.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/worker/src/Worker/Worker.csproj b/worker/src/Worker/Worker.csproj
index 03d43df..88e9a90 100644
--- a/worker/src/Worker/Worker.csproj
+++ b/worker/src/Worker/Worker.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>