4. Link multiple backends

This section details enabling communication between two Substra backends to allow them to exchange Functions and Models.

This can be achieved either at deployment time or when the backend is already deployed.

4.1. Update your Helm values

This guide assume that you have two organization in your network, one named ingen and the other biotechnica. The process would be the same if you have more organizations as we have to pair them. For example with three orgs you would repeat it for (org1, org2), (org1, org3) and (org2, org3).

In this setup we want ingen to exchange assets with biotechnica. We are assuming that you have two values files with the configuration for your existing deployment, one for each organization named: backend-ingen-values.yaml, backend-biotechnica-values.yaml.

Configure matching values for your 2 Organizations:

Create an account for MyOrg2 on MyOrg1. In backend-ingen-values.yaml, add the following content:
```
addAccountOperator:
  incomingOrganizations:
    - name: biotechnica
      secret: SECRET_ORG1_ORG2
      channel: our-channel
```
SECRET_ORG1_ORG2 is a password biotechnica needs to download assets from ingen.

our-channel was defined in the backend channel configuration – both ingen and biotechnica are members of it.

Create an account for ingen on biotechnica. In backend-biotechnica-values.yaml add the following content:

addAccountOperator:
  incomingOrganizations:
    - name: ingen
      secret: SECRET_ORG2_ORG1
      channel: our-channel

Configure ingen to use the right password when connecting to biotechnica. In backend-ingen-values.yaml add the following content under the addAccountOperator key:
```
outgoingOrganizations:
  - name: biotechnica
    secret: SECRET_ORG2_ORG1
```
SECRET_ORG2_ORG1 must naturally be the same as earlier.
Configure biotechnica to use the right password when connecting to ingen. In backend-biotechnica-values.yaml add the following content under the addAccountOperator key:
```
outgoingOrganizations:
  - name: ingen
    secret: SECRET_ORG1_ORG2
```

In the end your configuration files should have a section looking like this:

addAccountOperator:
  users: [...]
  incomingOrganizations:
    - name: biotechnica
      secret: SECRET_ORG1_ORG2
      channel: our-channel
  outgoingOrganizations:
    - name: biotechnica
      secret: SECRET_ORG2_ORG1

in backend-ingen-values.yaml, and:

addAccountOperator:
  users: [...]
  incomingOrganizations:
    - name: ingen
      secret: SECRET_ORG2_ORG1
      channel: our-channel
  outgoingOrganizations:
    - name: ingen
      secret: SECRET_ORG1_ORG2

in backend-biotechnica-values.yaml.

4.2. Deploy the updated chart

Let’s upgrade our previous deployments with the new values. We’ll run this twice, once on cluster-1 to update ingen and once on cluster-2 to update biotechnica:

helm upgrade RELEASE-NAME --namespace NAMESPACE substra/substra-backend --version VERSION --values VALUES-FILE

RELEASE-NAME and NAMESPACE must be the same as earlier, depending on the cluster.
You can retrieve them with helm list -A.
VERSION should be the same as earlier.
VALUES-FILE should be either backend-ingen-values.yaml or backend-biotechnica-values.yaml.

4.3. Validate that organizations are connected

We provide a small utility on the Substra backend server to test which organizations are accessible from the current organization. Follow these steps:

Connect to the Substra backend pod:

kubectl exec -it $(kubectl get pod -l "app.kubernetes.io/name=substra-backend-server" -o name) -- /bin/bash

This opens a shell on the backend server pod.

List all organizations defined in the outgoing list and their status:

./manage.py get_outgoing_organization

The output should look like this:

|    org_id   |           org_address          | http_status |
| biotechnica | http://api.cluster-2.DOMAIN:80 |     200     |

If there is an error while trying to connect to the node it will appear in the http_status column.