# Upstream repository priority order
<a name="repo-upstream-search-order"></a>

 When you request a package version from a repository with one or more upstream repositories, their priority corresponds to the order that they were listed when calling the `create-repository` or `update-repository` command. When the requested package version is found, the search stops, even if it didn't search all upstream repositories. For more information, see [Add or remove upstream repositories (AWS CLI)](repo-upstream-add.md#repo-upstream-add-cli). 

 Use the `describe-repository` command to see the priority order.

```
aws codeartifact describe-repository --repository {{my_repo}} --domain {{my_domain}} --domain-owner {{111122223333}}
```

 The result might be the following. It shows that the upstream repository priority is `upstream-1` first, `upstream-2` second, and `upstream-3` third. 

```
{
    "repository": {
        "name": "{{my_repo}}",
        "administratorAccount": "{{123456789012}}",
        "domainName": "{{my_domain}}",
        "domainOwner": "{{111122223333}}",
        "arn": "arn:aws:codeartifact:{{us-east-1}}:{{111122223333}}:repository/{{my_domain}}/{{my_repo}}",
        "description": "My new repository",
        "upstreams": [
            {
                "repositoryName": "{{upstream-1}}"
            },
            {
                "repositoryName": "{{upstream-2}}"
            },
            {
                "repositoryName": "{{upstream-3}}"
            }
        ],
        "externalConnections": []
    }
}
```

## Simple priority order example
<a name="upstream-priority-order-simple"></a>

 In the following diagram, the `my_repo` repository has three upstream repositories. The priority order of the upstream repositories is `upstream-1`, `upstream-2`, `upstream-3`. 

![Simple upstream repository diagram showing my_repo with 3 upstream repositories.](http://docs.aws.amazon.com/codeartifact/latest/ug/images/upstream-diagram-simple.png)


 A request for a package version in `my_repo` searches the repositories in the following order until it is found, or until an HTTP 404 `Not Found` response is returned to the client: 

1.  `my_repo` 

1.  `upstream-1` 

1.  `upstream-2` 

1.  `upstream-3` 

If the package version is found, the search stops, even if it didn't look in all upstream repositories. For example, if the package version is found in `upstream-1`, the search stops and CodeArtifact doesn't look in `upstream-2` or `upstream-3`. 

 When you use the AWS CLI command `list-package-versions` to list package versions in `my_repo`, it looks only in `my_repo`. It does not list package versions in upstream repositories. 

## Complex priority order example
<a name="upstream-search-order-complex"></a>

 If an upstream repository has its own upstream repositories, the same logic is used to find a package version before moving to the next upstream repository. For example, suppose that your `my_repo` repository has two upstream repositories, `A` and `B`. If repository `A` has upstream repositories, a request for a package version in `my_repo` first looks in `my_repo`, second in `A`, then in the upstream repositories of `A`, and so on. 

 In the following diagram, the `my_repo` repository contains upstream repositories. Upstream repository `A` has two upstream repositories, and `D` has one upstream repository. Upstream repositories at the same level in the diagram appear in their priority order, left to right (repository `A` has a higher priority order than repository `B`, and repository `C` has a higher priority order than repository `D`). 

![A more complex upstream repository diagram with 2 upstream repositories A and B and additional upstream repositories.](http://docs.aws.amazon.com/codeartifact/latest/ug/images/upstream-diagram-complex.png)


In this example, a request for a package version in `my_repo` looks in the repositories in the following order until it is found, or until a package manager returns an HTTP 404 `Not Found` response to the client: 

1.  `my_repo` 

1.  `A` 

1.  `C` 

1.  `D` 

1.  `E` 

1.  `B`