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I tried using `.get()` but it throws an error `Cannot call '.get' during update or preview`

You need to use `apply` for this - as in:

```
containerDefintiions: x.repositoryUrl.apply(repositoryUrl =&gt; JSON.stringify({ ... repositoryUrl ... }))
```

See <https://pulumi.io/reference/programming-model.html#apply> for some more notes related to this.

I saw that but `.apply` returns another output object

Right - but you can pass an `Output` as an `Input` to any resource - in particular as the `containerDefinitions`.

yes but i'm loading containerDefinitions from a json file

```let content = fs.readFileSync("task-definition.json");
const repo = new aws.ecr.Repository('flexkeygen', {});
const taskDefinition = new aws.ecs.TaskDefinition('flexkeygen_test', {
    containerDefinitions: JSON.stringify(taskDefinitionJson.taskDefinition.containerDefinitions),
    ...```

I might have to see more of your code to make a concrete suggestion.   As noted in the docs, you can't turn an `Output&lt;string&gt;` into a `string` - but you can do all the work needed to transofmr that output into the value that you need as n input inside an `apply`.

From the docs, `containerDefinitions` is a string

So I have my taskdefinition stored as a json file- i'd like to set the `image` registry URL with the ECR registryUrl,  is that not possible to do?

`containerDefinitions` is an `Input&lt;string&gt;`: <https://pulumi.io/reference/pkg/nodejs/@pulumi/aws/ecs/#TaskDefinitionArgs-containerDefinitions>

Which means you can pass a `string` *or* an `Output&lt;string&gt;`.

so theres no way to template it from a JSON file, I have to build the object?

How were you going to template it from a file?  You should be able to do all the same things - you just have to do them inside of an `apply`?

I exported the JSON definition with the `aws ecs describe-task-definition --task-definition flexkeygen_webapp:6 &gt; task-definition.json`

I want to reuse it for all accountIDs by replacing the registryUrl which changes based on AWS account ID

```
let taskDefinitionJson = JSON.parse(fs.readFileSync("task-definition.json").toString());
const repo = new aws.ecr.Repository('flexkeygen', {});
const taskDefinition = new aws.ecs.TaskDefinition('flexkeygen_test', {
    containerDefinitions: repo.rpositoryUrl.apply(repositoryUrl =&gt; {
        taskDefinitionJson.taskDefinition.containerDefinitions.something = repositoryUrl;
        return JSON.stringify(taskDefinitionJson.taskDefinition.containerDefinitions);
    }),
});
```

thanks!  i guess will have to deal with not being able to get values as strings - thanks for the clarification